thermochemistry
DESCRIPTION
Thermochemistry. By Sumana Ramakrishnan And Reema Sil. Thermochemistry is the study of heat change in chemical reactions. Endothermic is any process in which heat has to be supplied to the system from the surroundings. Exothermic - PowerPoint PPT PresentationTRANSCRIPT
ThermochemistryThermochemistryBy By
Sumana RamakrishnanSumana RamakrishnanAndAnd
Reema SilReema Sil
ThermochemistryThermochemistry is is the study of heat change the study of heat change in chemical reactionsin chemical reactions
ExothermicExothermicis any process that gives off
heat ndash transfers thermal energy from the system to the surroundings
Endothermic is any process in which heat
has to be supplied to the system from the surroundings
DCHeatBA
HeatDCBA
EnthalpyEnthalpy is used to quantify the heat flow into or out of a system in a process that occurs at constant pressure
tsreacproductsreaction HHH tan
Hproducts lt Hreactants Hproducts gt Hreactants
∆H lt 0
∆H gt 0
Exothermic(system gives off
heat)
Endothermic (system absorbs
heat)Heat (q) absorbed or released Tmcq
m mass of a given quantity in grams (g)c specific heat the amount of heat (q) required to raise the temperature of one gram of the substance by one degree Celsius (Jg-1degC-1)∆t = temperaturefinal ndash temperatureinitial (degC)
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l)
When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned according to the equation above 6498 kilojoules of heat is released Use according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followthe information in the table below to answer the questions that follow
Substance
Standard Heat of Formation ∆H˚ at
25˚C (kJmol) Absolute Entropy S˚
at 25˚C (JmolK)
C(graphite) 000 569
CO2(g) -3935 2136
H2(g) 000 1306
H2O(l) -28585 6991
O2(g) 000 2050
C6H5OH(s) 1440
(a) Calculate the molar heat of combustion of phenol in kilojoules per mole at 25˚C
(b) Calculate the standard heat of formation ∆H˚ of phenol in kilojoules per mole at 25˚C
(c) Calculate the value of the standard free-energy change ∆G˚ for the combustion of phenol at 25˚C
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely is completely burned according to the equation above 6498 kilojoules of heat is burned according to the equation above 6498 kilojoules of heat is
released released
(a) Calculate the molar heat of combustion of phenol in kilojoules per mole at 25˚C
combH
molarmassmass
kJ
The molar heat of combustion of The molar heat of combustion of phenol isphenol is
-3058 kilojoules-3058 kilojoules
mol
g
g
kJ
11394
0002
9864
molkJ3058
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(From (a) ∆Hrxn = -3058 kJ)
Substance
Standard Heat of Formation ∆H˚ at 25˚C
(kJmol)
C(graphite) 000
CO2(g) -3935
H2(g) 000
H2O(l) -28585
O2(g) 000
C6H5OH(s)
(b) Calculate the standard heat of formation ∆H˚ of phenol in kilojoules per mole at 25˚C
Equation
Variables
Numbers
tsreacproductsreaction HHH tan xOHCOH reaction 22 36 x 52853539363058
molkJx 161
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(c) (c) Calculate the value of the standard free-energy change ∆G˚ for the combustion of phenol at 25˚C
)tan()( tsreacproducts SSS First you must solve for ∆S
25622 736 OOHHCOHCO
0205701449169362136 J6787Then plug values into
STHG kJ0876702983058
kJ3032
STHG
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
01907 moles of
gaseous products
nRTPV
V
nRTP
L
Kmol molKatmL
10
38308206019070
atm5990
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
molCO
56
2
1
6
21270 molCO
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
OmolH
56
2
1
3 OmolH206370
nRTPV
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to NO is converted to NO22(g)(g)(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the temperature is increased Justify your answerremain unchanged as the temperature is increased Justify your answer
(c) Use the data in the table to calculate the value of the standard molar entropy S˚ for (c) Use the data in the table to calculate the value of the standard molar entropy S˚ for OO22(g)(g) at 25˚C at 25˚C
(d) Use the data in the table to calculate the bond energy in kJ mol(d) Use the data in the table to calculate the bond energy in kJ mol-1-1 of the of the nitrogen-oxygen bond in NOnitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are molecule are
equivalent (ie they have the same energy)equivalent (ie they have the same energy)
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to is converted to NONO22(g)(g)
gNO173
gNO
molNO
0130
1
molNO
kJ
2
1114 kJ97138
The reason our answer is negative is because the reaction is exothermic
Even though it results in a negative change in heat for the reaction
the amount of heat released is 13897kJ (a positive quantity)
So the answer to the question in part (a) is the positive quantity
13897 kJ
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C
eqKmolJ KKJ ln298314840070
eqKln428
eqKe 428
12101582 eqK
eqKRTG ln
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
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AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
ThermochemistryThermochemistry is is the study of heat change the study of heat change in chemical reactionsin chemical reactions
ExothermicExothermicis any process that gives off
heat ndash transfers thermal energy from the system to the surroundings
Endothermic is any process in which heat
has to be supplied to the system from the surroundings
DCHeatBA
HeatDCBA
EnthalpyEnthalpy is used to quantify the heat flow into or out of a system in a process that occurs at constant pressure
tsreacproductsreaction HHH tan
Hproducts lt Hreactants Hproducts gt Hreactants
∆H lt 0
∆H gt 0
Exothermic(system gives off
heat)
Endothermic (system absorbs
heat)Heat (q) absorbed or released Tmcq
m mass of a given quantity in grams (g)c specific heat the amount of heat (q) required to raise the temperature of one gram of the substance by one degree Celsius (Jg-1degC-1)∆t = temperaturefinal ndash temperatureinitial (degC)
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l)
When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned according to the equation above 6498 kilojoules of heat is released Use according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followthe information in the table below to answer the questions that follow
Substance
Standard Heat of Formation ∆H˚ at
25˚C (kJmol) Absolute Entropy S˚
at 25˚C (JmolK)
C(graphite) 000 569
CO2(g) -3935 2136
H2(g) 000 1306
H2O(l) -28585 6991
O2(g) 000 2050
C6H5OH(s) 1440
(a) Calculate the molar heat of combustion of phenol in kilojoules per mole at 25˚C
(b) Calculate the standard heat of formation ∆H˚ of phenol in kilojoules per mole at 25˚C
(c) Calculate the value of the standard free-energy change ∆G˚ for the combustion of phenol at 25˚C
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely is completely burned according to the equation above 6498 kilojoules of heat is burned according to the equation above 6498 kilojoules of heat is
released released
(a) Calculate the molar heat of combustion of phenol in kilojoules per mole at 25˚C
combH
molarmassmass
kJ
The molar heat of combustion of The molar heat of combustion of phenol isphenol is
-3058 kilojoules-3058 kilojoules
mol
g
g
kJ
11394
0002
9864
molkJ3058
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(From (a) ∆Hrxn = -3058 kJ)
Substance
Standard Heat of Formation ∆H˚ at 25˚C
(kJmol)
C(graphite) 000
CO2(g) -3935
H2(g) 000
H2O(l) -28585
O2(g) 000
C6H5OH(s)
(b) Calculate the standard heat of formation ∆H˚ of phenol in kilojoules per mole at 25˚C
Equation
Variables
Numbers
tsreacproductsreaction HHH tan xOHCOH reaction 22 36 x 52853539363058
molkJx 161
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(c) (c) Calculate the value of the standard free-energy change ∆G˚ for the combustion of phenol at 25˚C
)tan()( tsreacproducts SSS First you must solve for ∆S
25622 736 OOHHCOHCO
0205701449169362136 J6787Then plug values into
STHG kJ0876702983058
kJ3032
STHG
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
01907 moles of
gaseous products
nRTPV
V
nRTP
L
Kmol molKatmL
10
38308206019070
atm5990
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
molCO
56
2
1
6
21270 molCO
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
OmolH
56
2
1
3 OmolH206370
nRTPV
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to NO is converted to NO22(g)(g)(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the temperature is increased Justify your answerremain unchanged as the temperature is increased Justify your answer
(c) Use the data in the table to calculate the value of the standard molar entropy S˚ for (c) Use the data in the table to calculate the value of the standard molar entropy S˚ for OO22(g)(g) at 25˚C at 25˚C
(d) Use the data in the table to calculate the bond energy in kJ mol(d) Use the data in the table to calculate the bond energy in kJ mol-1-1 of the of the nitrogen-oxygen bond in NOnitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are molecule are
equivalent (ie they have the same energy)equivalent (ie they have the same energy)
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to is converted to NONO22(g)(g)
gNO173
gNO
molNO
0130
1
molNO
kJ
2
1114 kJ97138
The reason our answer is negative is because the reaction is exothermic
Even though it results in a negative change in heat for the reaction
the amount of heat released is 13897kJ (a positive quantity)
So the answer to the question in part (a) is the positive quantity
13897 kJ
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C
eqKmolJ KKJ ln298314840070
eqKln428
eqKe 428
12101582 eqK
eqKRTG ln
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
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AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
EnthalpyEnthalpy is used to quantify the heat flow into or out of a system in a process that occurs at constant pressure
tsreacproductsreaction HHH tan
Hproducts lt Hreactants Hproducts gt Hreactants
∆H lt 0
∆H gt 0
Exothermic(system gives off
heat)
Endothermic (system absorbs
heat)Heat (q) absorbed or released Tmcq
m mass of a given quantity in grams (g)c specific heat the amount of heat (q) required to raise the temperature of one gram of the substance by one degree Celsius (Jg-1degC-1)∆t = temperaturefinal ndash temperatureinitial (degC)
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l)
When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned according to the equation above 6498 kilojoules of heat is released Use according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followthe information in the table below to answer the questions that follow
Substance
Standard Heat of Formation ∆H˚ at
25˚C (kJmol) Absolute Entropy S˚
at 25˚C (JmolK)
C(graphite) 000 569
CO2(g) -3935 2136
H2(g) 000 1306
H2O(l) -28585 6991
O2(g) 000 2050
C6H5OH(s) 1440
(a) Calculate the molar heat of combustion of phenol in kilojoules per mole at 25˚C
(b) Calculate the standard heat of formation ∆H˚ of phenol in kilojoules per mole at 25˚C
(c) Calculate the value of the standard free-energy change ∆G˚ for the combustion of phenol at 25˚C
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely is completely burned according to the equation above 6498 kilojoules of heat is burned according to the equation above 6498 kilojoules of heat is
released released
(a) Calculate the molar heat of combustion of phenol in kilojoules per mole at 25˚C
combH
molarmassmass
kJ
The molar heat of combustion of The molar heat of combustion of phenol isphenol is
-3058 kilojoules-3058 kilojoules
mol
g
g
kJ
11394
0002
9864
molkJ3058
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(From (a) ∆Hrxn = -3058 kJ)
Substance
Standard Heat of Formation ∆H˚ at 25˚C
(kJmol)
C(graphite) 000
CO2(g) -3935
H2(g) 000
H2O(l) -28585
O2(g) 000
C6H5OH(s)
(b) Calculate the standard heat of formation ∆H˚ of phenol in kilojoules per mole at 25˚C
Equation
Variables
Numbers
tsreacproductsreaction HHH tan xOHCOH reaction 22 36 x 52853539363058
molkJx 161
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(c) (c) Calculate the value of the standard free-energy change ∆G˚ for the combustion of phenol at 25˚C
)tan()( tsreacproducts SSS First you must solve for ∆S
25622 736 OOHHCOHCO
0205701449169362136 J6787Then plug values into
STHG kJ0876702983058
kJ3032
STHG
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
01907 moles of
gaseous products
nRTPV
V
nRTP
L
Kmol molKatmL
10
38308206019070
atm5990
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
molCO
56
2
1
6
21270 molCO
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
OmolH
56
2
1
3 OmolH206370
nRTPV
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to NO is converted to NO22(g)(g)(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the temperature is increased Justify your answerremain unchanged as the temperature is increased Justify your answer
(c) Use the data in the table to calculate the value of the standard molar entropy S˚ for (c) Use the data in the table to calculate the value of the standard molar entropy S˚ for OO22(g)(g) at 25˚C at 25˚C
(d) Use the data in the table to calculate the bond energy in kJ mol(d) Use the data in the table to calculate the bond energy in kJ mol-1-1 of the of the nitrogen-oxygen bond in NOnitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are molecule are
equivalent (ie they have the same energy)equivalent (ie they have the same energy)
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to is converted to NONO22(g)(g)
gNO173
gNO
molNO
0130
1
molNO
kJ
2
1114 kJ97138
The reason our answer is negative is because the reaction is exothermic
Even though it results in a negative change in heat for the reaction
the amount of heat released is 13897kJ (a positive quantity)
So the answer to the question in part (a) is the positive quantity
13897 kJ
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C
eqKmolJ KKJ ln298314840070
eqKln428
eqKe 428
12101582 eqK
eqKRTG ln
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
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Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l)
When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned according to the equation above 6498 kilojoules of heat is released Use according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followthe information in the table below to answer the questions that follow
Substance
Standard Heat of Formation ∆H˚ at
25˚C (kJmol) Absolute Entropy S˚
at 25˚C (JmolK)
C(graphite) 000 569
CO2(g) -3935 2136
H2(g) 000 1306
H2O(l) -28585 6991
O2(g) 000 2050
C6H5OH(s) 1440
(a) Calculate the molar heat of combustion of phenol in kilojoules per mole at 25˚C
(b) Calculate the standard heat of formation ∆H˚ of phenol in kilojoules per mole at 25˚C
(c) Calculate the value of the standard free-energy change ∆G˚ for the combustion of phenol at 25˚C
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely is completely burned according to the equation above 6498 kilojoules of heat is burned according to the equation above 6498 kilojoules of heat is
released released
(a) Calculate the molar heat of combustion of phenol in kilojoules per mole at 25˚C
combH
molarmassmass
kJ
The molar heat of combustion of The molar heat of combustion of phenol isphenol is
-3058 kilojoules-3058 kilojoules
mol
g
g
kJ
11394
0002
9864
molkJ3058
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(From (a) ∆Hrxn = -3058 kJ)
Substance
Standard Heat of Formation ∆H˚ at 25˚C
(kJmol)
C(graphite) 000
CO2(g) -3935
H2(g) 000
H2O(l) -28585
O2(g) 000
C6H5OH(s)
(b) Calculate the standard heat of formation ∆H˚ of phenol in kilojoules per mole at 25˚C
Equation
Variables
Numbers
tsreacproductsreaction HHH tan xOHCOH reaction 22 36 x 52853539363058
molkJx 161
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(c) (c) Calculate the value of the standard free-energy change ∆G˚ for the combustion of phenol at 25˚C
)tan()( tsreacproducts SSS First you must solve for ∆S
25622 736 OOHHCOHCO
0205701449169362136 J6787Then plug values into
STHG kJ0876702983058
kJ3032
STHG
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
01907 moles of
gaseous products
nRTPV
V
nRTP
L
Kmol molKatmL
10
38308206019070
atm5990
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
molCO
56
2
1
6
21270 molCO
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
OmolH
56
2
1
3 OmolH206370
nRTPV
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to NO is converted to NO22(g)(g)(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the temperature is increased Justify your answerremain unchanged as the temperature is increased Justify your answer
(c) Use the data in the table to calculate the value of the standard molar entropy S˚ for (c) Use the data in the table to calculate the value of the standard molar entropy S˚ for OO22(g)(g) at 25˚C at 25˚C
(d) Use the data in the table to calculate the bond energy in kJ mol(d) Use the data in the table to calculate the bond energy in kJ mol-1-1 of the of the nitrogen-oxygen bond in NOnitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are molecule are
equivalent (ie they have the same energy)equivalent (ie they have the same energy)
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to is converted to NONO22(g)(g)
gNO173
gNO
molNO
0130
1
molNO
kJ
2
1114 kJ97138
The reason our answer is negative is because the reaction is exothermic
Even though it results in a negative change in heat for the reaction
the amount of heat released is 13897kJ (a positive quantity)
So the answer to the question in part (a) is the positive quantity
13897 kJ
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C
eqKmolJ KKJ ln298314840070
eqKln428
eqKe 428
12101582 eqK
eqKRTG ln
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
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CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely is completely burned according to the equation above 6498 kilojoules of heat is burned according to the equation above 6498 kilojoules of heat is
released released
(a) Calculate the molar heat of combustion of phenol in kilojoules per mole at 25˚C
combH
molarmassmass
kJ
The molar heat of combustion of The molar heat of combustion of phenol isphenol is
-3058 kilojoules-3058 kilojoules
mol
g
g
kJ
11394
0002
9864
molkJ3058
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(From (a) ∆Hrxn = -3058 kJ)
Substance
Standard Heat of Formation ∆H˚ at 25˚C
(kJmol)
C(graphite) 000
CO2(g) -3935
H2(g) 000
H2O(l) -28585
O2(g) 000
C6H5OH(s)
(b) Calculate the standard heat of formation ∆H˚ of phenol in kilojoules per mole at 25˚C
Equation
Variables
Numbers
tsreacproductsreaction HHH tan xOHCOH reaction 22 36 x 52853539363058
molkJx 161
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(c) (c) Calculate the value of the standard free-energy change ∆G˚ for the combustion of phenol at 25˚C
)tan()( tsreacproducts SSS First you must solve for ∆S
25622 736 OOHHCOHCO
0205701449169362136 J6787Then plug values into
STHG kJ0876702983058
kJ3032
STHG
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
01907 moles of
gaseous products
nRTPV
V
nRTP
L
Kmol molKatmL
10
38308206019070
atm5990
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
molCO
56
2
1
6
21270 molCO
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
OmolH
56
2
1
3 OmolH206370
nRTPV
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to NO is converted to NO22(g)(g)(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the temperature is increased Justify your answerremain unchanged as the temperature is increased Justify your answer
(c) Use the data in the table to calculate the value of the standard molar entropy S˚ for (c) Use the data in the table to calculate the value of the standard molar entropy S˚ for OO22(g)(g) at 25˚C at 25˚C
(d) Use the data in the table to calculate the bond energy in kJ mol(d) Use the data in the table to calculate the bond energy in kJ mol-1-1 of the of the nitrogen-oxygen bond in NOnitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are molecule are
equivalent (ie they have the same energy)equivalent (ie they have the same energy)
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to is converted to NONO22(g)(g)
gNO173
gNO
molNO
0130
1
molNO
kJ
2
1114 kJ97138
The reason our answer is negative is because the reaction is exothermic
Even though it results in a negative change in heat for the reaction
the amount of heat released is 13897kJ (a positive quantity)
So the answer to the question in part (a) is the positive quantity
13897 kJ
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C
eqKmolJ KKJ ln298314840070
eqKln428
eqKe 428
12101582 eqK
eqKRTG ln
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
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Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(From (a) ∆Hrxn = -3058 kJ)
Substance
Standard Heat of Formation ∆H˚ at 25˚C
(kJmol)
C(graphite) 000
CO2(g) -3935
H2(g) 000
H2O(l) -28585
O2(g) 000
C6H5OH(s)
(b) Calculate the standard heat of formation ∆H˚ of phenol in kilojoules per mole at 25˚C
Equation
Variables
Numbers
tsreacproductsreaction HHH tan xOHCOH reaction 22 36 x 52853539363058
molkJx 161
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(c) (c) Calculate the value of the standard free-energy change ∆G˚ for the combustion of phenol at 25˚C
)tan()( tsreacproducts SSS First you must solve for ∆S
25622 736 OOHHCOHCO
0205701449169362136 J6787Then plug values into
STHG kJ0876702983058
kJ3032
STHG
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
01907 moles of
gaseous products
nRTPV
V
nRTP
L
Kmol molKatmL
10
38308206019070
atm5990
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
molCO
56
2
1
6
21270 molCO
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
OmolH
56
2
1
3 OmolH206370
nRTPV
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to NO is converted to NO22(g)(g)(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the temperature is increased Justify your answerremain unchanged as the temperature is increased Justify your answer
(c) Use the data in the table to calculate the value of the standard molar entropy S˚ for (c) Use the data in the table to calculate the value of the standard molar entropy S˚ for OO22(g)(g) at 25˚C at 25˚C
(d) Use the data in the table to calculate the bond energy in kJ mol(d) Use the data in the table to calculate the bond energy in kJ mol-1-1 of the of the nitrogen-oxygen bond in NOnitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are molecule are
equivalent (ie they have the same energy)equivalent (ie they have the same energy)
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to is converted to NONO22(g)(g)
gNO173
gNO
molNO
0130
1
molNO
kJ
2
1114 kJ97138
The reason our answer is negative is because the reaction is exothermic
Even though it results in a negative change in heat for the reaction
the amount of heat released is 13897kJ (a positive quantity)
So the answer to the question in part (a) is the positive quantity
13897 kJ
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C
eqKmolJ KKJ ln298314840070
eqKln428
eqKe 428
12101582 eqK
eqKRTG ln
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
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AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(c) (c) Calculate the value of the standard free-energy change ∆G˚ for the combustion of phenol at 25˚C
)tan()( tsreacproducts SSS First you must solve for ∆S
25622 736 OOHHCOHCO
0205701449169362136 J6787Then plug values into
STHG kJ0876702983058
kJ3032
STHG
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
01907 moles of
gaseous products
nRTPV
V
nRTP
L
Kmol molKatmL
10
38308206019070
atm5990
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
molCO
56
2
1
6
21270 molCO
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
OmolH
56
2
1
3 OmolH206370
nRTPV
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to NO is converted to NO22(g)(g)(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the temperature is increased Justify your answerremain unchanged as the temperature is increased Justify your answer
(c) Use the data in the table to calculate the value of the standard molar entropy S˚ for (c) Use the data in the table to calculate the value of the standard molar entropy S˚ for OO22(g)(g) at 25˚C at 25˚C
(d) Use the data in the table to calculate the bond energy in kJ mol(d) Use the data in the table to calculate the bond energy in kJ mol-1-1 of the of the nitrogen-oxygen bond in NOnitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are molecule are
equivalent (ie they have the same energy)equivalent (ie they have the same energy)
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to is converted to NONO22(g)(g)
gNO173
gNO
molNO
0130
1
molNO
kJ
2
1114 kJ97138
The reason our answer is negative is because the reaction is exothermic
Even though it results in a negative change in heat for the reaction
the amount of heat released is 13897kJ (a positive quantity)
So the answer to the question in part (a) is the positive quantity
13897 kJ
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C
eqKmolJ KKJ ln298314840070
eqKln428
eqKe 428
12101582 eqK
eqKRTG ln
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
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AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
CC66HH55OHOH(s)(s) + 7 O + 7 O22(g)(g) rarr 6 CO rarr 6 CO22(g)(g) + 3 H + 3 H22OO(l)(l) When a 2000-gram sample of pure phenol CWhen a 2000-gram sample of pure phenol C66HH55OHOH(s)(s) is completely burned is completely burned
according to the equation above 6498 kilojoules of heat is released Use the according to the equation above 6498 kilojoules of heat is released Use the information in the table below to answer the questions that followinformation in the table below to answer the questions that follow
(d) If the volume of the combustion container is 100 liters calculate the final pressure in the container when the temperature is changed to 110˚C (Assume no oxygen remains unreacted and that all products are gaseous)
01907 moles of
gaseous products
nRTPV
V
nRTP
L
Kmol molKatmL
10
38308206019070
atm5990
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
molCO
56
2
1
6
21270 molCO
OHHgC 560002
OHHgC
OHHmolC
56
56
1294
1
OHHmolC
OmolH
56
2
1
3 OmolH206370
nRTPV
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to NO is converted to NO22(g)(g)(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the temperature is increased Justify your answerremain unchanged as the temperature is increased Justify your answer
(c) Use the data in the table to calculate the value of the standard molar entropy S˚ for (c) Use the data in the table to calculate the value of the standard molar entropy S˚ for OO22(g)(g) at 25˚C at 25˚C
(d) Use the data in the table to calculate the bond energy in kJ mol(d) Use the data in the table to calculate the bond energy in kJ mol-1-1 of the of the nitrogen-oxygen bond in NOnitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are molecule are
equivalent (ie they have the same energy)equivalent (ie they have the same energy)
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to is converted to NONO22(g)(g)
gNO173
gNO
molNO
0130
1
molNO
kJ
2
1114 kJ97138
The reason our answer is negative is because the reaction is exothermic
Even though it results in a negative change in heat for the reaction
the amount of heat released is 13897kJ (a positive quantity)
So the answer to the question in part (a) is the positive quantity
13897 kJ
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C
eqKmolJ KKJ ln298314840070
eqKln428
eqKe 428
12101582 eqK
eqKRTG ln
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to NO is converted to NO22(g)(g)(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the temperature is increased Justify your answerremain unchanged as the temperature is increased Justify your answer
(c) Use the data in the table to calculate the value of the standard molar entropy S˚ for (c) Use the data in the table to calculate the value of the standard molar entropy S˚ for OO22(g)(g) at 25˚C at 25˚C
(d) Use the data in the table to calculate the bond energy in kJ mol(d) Use the data in the table to calculate the bond energy in kJ mol-1-1 of the of the nitrogen-oxygen bond in NOnitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are molecule are
equivalent (ie they have the same energy)equivalent (ie they have the same energy)
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to is converted to NONO22(g)(g)
gNO173
gNO
molNO
0130
1
molNO
kJ
2
1114 kJ97138
The reason our answer is negative is because the reaction is exothermic
Even though it results in a negative change in heat for the reaction
the amount of heat released is 13897kJ (a positive quantity)
So the answer to the question in part (a) is the positive quantity
13897 kJ
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C
eqKmolJ KKJ ln298314840070
eqKln428
eqKe 428
12101582 eqK
eqKRTG ln
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
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2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(a) Calculate the quantity of heat released when 731 g of NO(a) Calculate the quantity of heat released when 731 g of NO(g)(g) is converted to is converted to NONO22(g)(g)
gNO173
gNO
molNO
0130
1
molNO
kJ
2
1114 kJ97138
The reason our answer is negative is because the reaction is exothermic
Even though it results in a negative change in heat for the reaction
the amount of heat released is 13897kJ (a positive quantity)
So the answer to the question in part (a) is the positive quantity
13897 kJ
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C
eqKmolJ KKJ ln298314840070
eqKln428
eqKe 428
12101582 eqK
eqKRTG ln
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(i) Calculate the value of the equilibrium constant K(i) Calculate the value of the equilibrium constant Keqeq for the reaction at 25˚C for the reaction at 25˚C
eqKmolJ KKJ ln298314840070
eqKln428
eqKe 428
12101582 eqK
eqKRTG ln
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ(b) For the reaction at 25˚C the value of the standard free-energy change ∆G˚ is -704 kJ
(ii) Indicate whether the value of ∆G˚ would become more negative less negative or (ii) Indicate whether the value of ∆G˚ would become more negative less negative or remain unchanged as the remain unchanged as the temperature is increased Justify your answertemperature is increased Justify your answer
As T increases the quantity T∆S becomes As T increases the quantity T∆S becomes more and more negativemore and more negative
According to the equation subtracting a According to the equation subtracting a large negative number (T∆S) from another large negative number (T∆S) from another
negative number (∆H) is the same as negative number (∆H) is the same as addingadding a value to the negative ∆H making a value to the negative ∆H making
∆G˚ less negative∆G˚ less negative
∆∆G˚ will become less negative because of G˚ will become less negative because of the roles of ∆H T and ∆S in the equationthe roles of ∆H T and ∆S in the equation
STHG
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(c) Use the data in the table below to calculate the value of the standard molar (c) Use the data in the table below to calculate the value of the standard molar entropy S˚ for Oentropy S˚ for O22(g)(g) at 25˚C at 25˚C
Standard Molar Standard Molar Entropy S˚ Entropy S˚
(J K(J K-1-1 mol mol-1-1))
NONO(g)(g) 21082108
NONO22(g)(g) 24012401
∆S˚ = sum S˚products - sum S˚reactants
The standard molar entropy for O2(g) is 2051 J K-1 mol-1
22 22 OSNOSNOSS xS 82102124025146
molKJx 1205642124805146
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
2 NO2 NO(g)(g) + O + O22(g)(g) rarr 2 NOrarr 2 NO22(g)(g) ∆H˚= -1141 kJ ∆S˚= -1465 J K∆H˚= -1141 kJ ∆S˚= -1465 J K-1-1
The reaction represented above is one that contributes significantly to the The reaction represented above is one that contributes significantly to the formation of photochemical smogformation of photochemical smog
(d) Use the data in the table below to calculate the bond energy in kJ mol(d) Use the data in the table below to calculate the bond energy in kJ mol -1-1 of of the nitrogen-oxygen bond in NOthe nitrogen-oxygen bond in NO22 Assume that the bonds in the NO Assume that the bonds in the NO22 molecule are equivalent (ie they have the same energy)molecule are equivalent (ie they have the same energy)
Bond EnergyBond Energy
(kJ mol(kJ mol-1-1))
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO 607607
Oxygen-oxygen bond in OOxygen-oxygen bond in O22 495495
Nitrogen-oxygen bond in NONitrogen-oxygen bond in NO22
(bonds of reactants are broken bonds of products are formed)
dbondsformenbondsbroke HHH
ctsbondsprodutsbondsreac HHH tan
molkJx 5911rarr
In this equation x represents the total bond energy in an NO2 molecule Since there are
two N-O bonds in NO2 x divided by two equals the bond energy of each N-O bond in
the molecule
xkJH 249560721114
molkJmol
kJx775455
2
5911
2
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
Answer the following questions that relate to the Answer the following questions that relate to the chemistry of nitrogenchemistry of nitrogen
(a) Two nitrogen atoms combine to (a) Two nitrogen atoms combine to form a nitrogen molecule as form a nitrogen molecule as represented by the below equation represented by the below equation Using the table of average bond Using the table of average bond energies determine the enthalpy energies determine the enthalpy change ∆H for the reactionchange ∆H for the reaction
)(2)(2 gg NN
BondBond Average Bond Average Bond Energy (kJ molEnergy (kJ mol-1-1))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
(b) The reaction between nitrogen and hydrogen to from ammonia is (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the standard entropy change represented below Predict the sign of the standard entropy change ∆S˚ for the reaction Justify your answer∆S˚ for the reaction Justify your answer
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high temperatures negative at low temperatures but positive at high temperatures ExplainExplain
(d) When N(d) When N22(g)(g) and Hand H22(g)(g) are placed in a sealed contained at a low are placed in a sealed contained at a low temperature no measurable amount of NHtemperature no measurable amount of NH33(g)(g) is produced Explain is produced Explain
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
(a) Two nitrogen atoms combine to form a nitrogen molecule (a) Two nitrogen atoms combine to form a nitrogen molecule as represented by the below equation Using the table of as represented by the below equation Using the table of
average bond energies determine the enthalpy change ∆H average bond energies determine the enthalpy change ∆H for the reactionfor the reaction
)(2)(2 gg NN
BondBondAverage Bond Average Bond Energy (kJ molEnergy (kJ mol--
11))
N-NN-N 160160
N=NN=N 420420
NN==NN 950950
dbondsformenbondsbroke HHH
kJH molkJ 9509500
The enthalpy change when two nitrogen atoms combine is -950 kJ The reaction only forms bonds which requires heat
energy
This makes the equation endothermic because it requires a heat supply to form N2(g)
(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
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(b) The reaction between nitrogen and hydrogen to from (b) The reaction between nitrogen and hydrogen to from ammonia is represented below Predict the sign of the ammonia is represented below Predict the sign of the
standard entropy change ∆S˚ for the reaction Justify your standard entropy change ∆S˚ for the reaction Justify your answeranswer
∆∆S˚S˚ (change in entropy) is the measure of disorder in a reaction This measure of entropy can be judged by the change in moles of gaseous particles
In this reaction since there are fewer gaseous moles of products than there are gaseous moles of reactants there is a decrease in disorder - meaning ∆S is negative for this reaction
)(3)(2)(2 23 ggg NHHN ∆H˚= -922 kJ
productstsreac MolesGasMolesGas tan
productstsreac MolesGasMolesGas tan
SinEntropyMolesGas
SinEntropyMolesGas
(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
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(c) The value of ∆G˚ for the reaction represented in part (b) is (c) The value of ∆G˚ for the reaction represented in part (b) is negative at low temperatures but positive at high negative at low temperatures but positive at high
temperatures Explaintemperatures Explain
The value of ∆G free energy is determined by the value of ∆H ndash T(∆S) We determined that both ∆H and ∆S are negative (from part b) and T will always be positive (because temperature in Kelvin is never negative
If T is a small value T(∆S) will not be large enough to overcome ∆H Thus ∆G will be negative
If T is a large value then T(∆S) will be large enough to overcome ∆H and make ∆G positive
So subtracting the negative value of T(∆S) from ∆H can result in either a negative or positive number
STHG
eL
Small
arg
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
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AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
(d) When N(d) When N22(g) (g) and Hand H22(g)(g) are placed in a sealed are placed in a sealed contained at a low temperature no measurable contained at a low temperature no measurable
amount of NHamount of NH33(g)(g) is produced Explain is produced Explain
As we determined in Part C when at a low temperature ∆G is negative When ∆G is negative it means that the reaction is spontaneous proceeding in the forward direction on its own
However if the reaction does not seem to visibly proceed it does not mean that the reaction is not spontaneous
There are two reasons for why a measurable amount of NH3(g) is not observed- All reactions require a certain activation energy to initiate the
reaction If a reaction does not have that required energy the reaction will remain inert even if it is spontaneous
- The reaction might require an extensive amount of time to proceed Because the reaction is so slow the amount of NH3(g) produced may not be immediately visible but the reaction continues to occur
)(3)(2)(2 23 ggg NHHN
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
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Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of
water
(a) Give appropriate units for each of the terms in the equation q = mc ∆T(b) List the measurements that must be made in order to obtain the value of q(c) Explain how to calculate each of the following
I The number of moles of water formed during the experimentII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your predictionII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
(e) Suppose that a significant amount of heat were lost to the air during the experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
)(2)()( laqaq OHOHH
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
Tmcq (a) Give appropriate units for each of the terms in the equation q = mc ∆T
CaloriesKilojoules GramsKilo
Kg
Jor
Cg
J
KC
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(b) List the measurements that must be made in order to obtain the value of q
1 Volume or mass of the HCl and NaOH solutions2 Initial temperature of HCl and NaOH before mixing
3 Final temperature of HCl and NaOH after mixing
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingI The number of moles of water formed during the experiment
)(2)()( laqaq OHOHH
- Or -
OmolH
molHCl
OmolH
L
molHClvolumeHCl 2
2
1
1
1
01
OmolH
molNaOH
OmolH
L
molNaOHvolumeNaOH 2
2
1
1
1
01
You could also reason that both HCl and NaOH react in a 11 ratio to form the same number of moles of water
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
(c) Explain how to calculate each of the followingII The value of the molar enthalpy of neutralization ∆Hneut for the reaction between HCl(aq) and NaOH(aq)
First you must solve for the heat produced using q=cm ∆T Then dividing this value by the moles of H2O (from part I)
OmolH
qH neut
2
This gives you the molar enthalpy of neutralization for the reaction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
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A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combinedThe densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as that of water
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHI Indicate whether the value of q increases decreases or stays the same when compared to the first experiment Justify your prediction
Tmcq You can reason that since more moles of HCl and NaOH are reacting
the final temperature of the mixture will be higher
So ∆T will be greater which will increase q
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
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Jack WangJack Wang
(d) The student repeats the experiment with the same equal volumes as before but this time uses 20 M HCl and 20M NaOHII Indicate whether the value of the molar enthalpy of neutralization ∆Hneut increases decreases or stays the same when compared to the first experiment Justify your prediction
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water
As done in part C II the molar enthalpy is found by dividing q by the moles of water In the reaction both q and water increase proportionally by x
OmolHx
qxH neut
2
OmolH
q
2
Since x drops out you can see that the value of the molar enthalpy of neutralization remains the same as in the first experiment
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
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AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
A student is asked to determine the molar enthalpy of neutralization ∆Hneut for the reaction represented above The student combines equal volumes of 10M HCl and 10 M NaOH in an open polystyrene cup calorimeter The heat released by the reaction is determined by using the equation q=mc ∆TAssume the following
Both solutions are at the same temperature before they are combined
The densities of all the solutions are the same that of waterAny heat lost to the calorimeter of to the air is negligibleThe specific heat capacity of the combined solutions is the same as
that of water(e) Suppose that a significant amount of heat were lost to the air during the
experiment What effect would that have on the calculated value of the molar enthalpy of neutralization ∆Hneut Justify your answer
Heat lost to the air will decrease ∆T ndash which in turn equals a smaller q
Thus when you divide q by the number of moles of H2O ∆Hneut will be a smaller value
Tmcq
OmolH
qH neut
2
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang
The EndThe End
Voices by Sumana Ramakrishnan Voices by Sumana Ramakrishnan and Reema Siland Reema Sil
Powerpoint by Reema SilPowerpoint by Reema Sil
AP Problems painstakingly solved by bothAP Problems painstakingly solved by both
Special Thanks toSpecial Thanks toMr GangluffMr Gangluff
Mr AmendolaMr AmendolaEric LiuEric Liu
Jack WangJack Wang