ch. 10.4 and 11 thermodynamics
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Ch. 10.4 and 11 Thermodynamics. You must turn in your notes. Energy. Definition: the capacity to do work, or to produce heat; SI (metric) unit is J oule Non-SI unit is cal orie 1 cal = 4.18 J 1 calorie = the amount of energy needed to raise 1 gram of water 1° C - PowerPoint PPT PresentationTRANSCRIPT
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Ch. 10.4 and 11ThermodynamicsYou must turn in your notes
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Energy Definition: the capacity to do work, or to produce heat;
SI (metric) unit is Joule Non-SI unit is calorie
1 cal = 4.18 J 1 calorie = the amount of energy needed to raise 1
gram of water 1° C Heat - energy that is transferred from a warm
object to a cooler object; represented by “q” Temperature - a measure of the average kinetic
energy of an object
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Specific heat/Change of Temp
Quantity of heat needed to raise 1 gram of a substance 1° C; unit is J/g°C FORMULA: q= c x m x ΔT q= heat (J) c = specific heat (J/g°C) m = mass (g) T = change in temp. (°C)
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Specific Heat Practice Problem #1
1. Calculate the amount of heat in joules needed to warm 250. g of water from 25.0°C to 95.0°C. (c=4.184 J/°C g)
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Practice Problem #2
How much heat is lost when 50.0 grams of Al is cooled from 130.0 °C to 62.0 °C? The specific heat of Al is 0.897 J/g°C
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Change of state and heat
heat of fusion- amount of heat needed to melt 1 gram of a substance at its melting point
Hf copper = 205 J/g Hf water = 80 cal/g= 334 J/g q = mHf heat of vaporization- amount of heat needed to
boil 1 gram of a substance at its boiling point Hv water = 540 cal/g = 2260 J/g q= mHv
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Heating/Cooling Curves
Change of Phase
Change of Temperature
Know which formula to use when!
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Change of state Practice Problems
1. Calculate the amount of heat, in Joules, needed to melt 70.0g of copper at its melting point.
2. Calculate the heat required, in calories, to change 250g of water at 100°C to steam at 100°C.
3. Calculate the amount of heat needed to change 20g of ice at -10.0°C to water at 80.0°C.
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Enthalpy (H) a measure of heat content of a system H = change in heat content that accompanies a
process Hrxn = Hfinal - Hinitial
Hrxn = Hproducts - Hreactants
** ΔHrxn can also be written as ΔHf, for heat of formation**
**Chemical systems in the world tend to achieve the lowest possible energy. Would this occur in an exothermic or an endothermic reaction?
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Exothermic reactions
chemicals react and give off heat (feel hot); H is negative; products are more stable
4Fe + 3O2 2Fe2O3 + 1625 kJ
reactants
products
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Endothermic reactions
chemicals need to absorb energy in order for the reaction to take place (feel cool); H is positive; reactants are more stable
27 kJ + NH4NO3 NH4+ + NO3
-
products
reactants
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Practice problems #1
CO (g) + NO (g) CO2 (g) + N2 (g)
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Practice #2
CH4 (g)+ O2 (g) CO2 (g)+ H2O (g)
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Practice #3
N2 (g) + O2 (g) NO2 (g)
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Entropy (S)
Measure of disorder or chaos in a system Law of disorder – states that things move
spontaneously in the direction of maximum chaos or disorder
ΔSsystem = SP - SR If ΔS is +, there is an increase in entropy. If ΔS is -, there is a decrease in entropy
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Rules for disorder 1. Entropy increases as particles move apart.
Gas > Liquid > Solid I2 (s) I2 (g)
2. Entropy increases when you divide a substance into parts (when the total number of products > the total number of reactants)
2H2O 2H2 + O2
3. Entropy increases as temp increases b/c particles move faster. (unit for entropy is J/K mole)
4. Entropy increases when you dissolve a solid into a liquid. Entropy decreases when you dissolve a gas into a liquid.
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Entropy Examples
Water (liquid) - water (solid)
KCl(s) KCl (l)
C(s) + O2 (g) CO2 (g)
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Gibbs’ Free Energy (G)
Energy available to do work Relates enthalpy (H) and entropy (S),
using the equation: ΔG = ΔH – TΔS
ΔG = GP - GR
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Still confused?
Try these online notes http://www.sciencegeek.net/Chemistry/Po
werpoint/Unit7/Unit7_files/frame.htm
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Spontaneous Reactions
If ΔG is negative, the reaction will occur spontaneously.
If ΔG is positive, the reaction will NOT occur spontaneously.
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Quick Spontaneous Chart
ΔH - + + -
ΔS + - + -
ΔG - + Depends on temp
Depends on temp
spontaneous Non-
spontaneous