ch18.1 – reaction rates reaction rates explained by collision theory

Ch18.1 – Reaction RatesReaction Rates explained by collision theory.

-must collide with the correct orientation

-must have enough Kinetic energy to break apart old bonds when collide.

http://www.saskschools.ca/curr_content/chem30_05/2_kinetics/kinetics2_1.htm

Factors Affecting Reaction Rates“CANTC”

Concentration – more particles = more collision Surface Area – more surface area= more places for rxn to occurNature of the reactants – some substances are more reactive than othersTemperature – higher temp= more KE A.E.Catalyst – Lowers activation energy

(provides an alternate path) R P

Factors Affecting Reaction Rates“CANTC”

Concentration – more particles = more collision Surface Area – more surface area= more places for rxn to occurNature of the reactants – some substances are more reactive than othersTemperature – higher temp= more KE A.E.Catalyst – Lowers activation energy

(provides an alternate path) R P

Two Types of Catalysts: 1. Heterogeneous catalyst-

A surface for the reaction to take place on. (Like a work bench) Platinum is the most common.

2. Homogeneous catalyst-get involved in the reaction form intermediate compounds, but come back out unchanged.

The decomposition of hydrogen peroxide is slow. Iodide ions help speed it up.

H202(l) H20(l) + 02(g)

Reversible Reactions

2SO2(g) + O2(g) 2SO3(g)

1% 99%Forward & reverse reactions occurring at same time.

When they reach the same rate, reach chemical equilibrium.

- Doesn’t have to occur in the middle (50%,50%)

Exs) H2CO3 CO2 + H2O At equilibrioum,Products favored

1% 99%

CaCO3 CaO + CO2 At equilibrioum,Reactants favored

99% 1%Ch18 HW#1 1 - 6

Ch18 HW#1 1 – 61. Rate of reaction –

2. 1.0 mol zinc is completely converted to zinc oxide ZnO is 5.3 months.What is the average rate of conversion in mol/months

3. Refrigerated food vs. room temp food

Ch18 HW#1 1 – 61. Rate of reaction – how fast the reaction converts reactants into products

monthmol

months

mol19.0

Lower temp, Higher temp = higher KE slows rxn rate = higher rate of rxn

monthmol

months

mol19.0

4.How does each affect rate of reaction?a. Tempb. Concentrationc. Particle sized. Catalyst

5. Double arrows in equation:

6.How do the amounts of reactants & products change once a reactionhas achieved equilibrium?

4.How does each affect rate of reaction?a. Temp – higher temp = higher KE = faster rateb. Concentration – greater concentration = faster ratec. Particle size – smaller particles =more surface area = faster rated. Catalyst – lowers the activation energy = faster rate

Represent a reversible reaction.

N2(g) + 3H2(g) 2NH2(g)

Represent a reversible reaction.

The amounts stay constant. The rate of the forward reaction equals the rate of the reverse reaction.

N2(g) + 3H2(g) 2NH2(g)

Ch18.2 – Factors Affecting EquilibriumA chemical reaction that has reached equilibrium is a delicate balance. If it’s disturbed, it will make minute adjustments to restore itself at a new equilibrium position.

Le Chatelier’s PrincipleIf stress is applied to a system at equilibrium, the system changes to relieve the stress.

- Add something shifts to opposite side- Remove something shifts to the side of removal.- Adding pressure shifts to side with fewer gas particles.

Decreasing pressure shifts to side with more gas.

Ex1) N2(g) + 3H2(g) 2NH3(g) + heat

Remove NH3(g), shifts to ________Add N2: ________Add heat: ________Increase pressure: ________

Ex2) CO2(g) + H2(g) + heat CO(g) + H2O(g)

Decrease temp: ________Add heat: ________Add H2O: ________Increase pressure: ________

Ex1) N2(g) + 3H2(g) 2NH3(g) + heat

Remove NH3(g), shifts to productsAdd N2: productsAdd heat: reactantsIncrease pressure: products

Ex2) CO2(g) + H2(g) + heat CO(g) + H2O(g)

Decrease temp: reactantsAdd heat: productsAdd H2O: reactantsIncrease pressure: no affect

Ex3) 2 SO2(g) + O2(g) 2 SO3(g) + heat

Increase SO2 : ________

Increase heat: ________

Add SO3 : ________Increase pressure : ________

Ch18 HW#2

Lab18.1 – Reaction Rates

- due in 2 days

- Ch18 HW#2 due at beginning of period

Ch18.1,18.2 Review Worksheet1. CANTC:

2. What do catalysts do to speed up a reaction?

3. Draw catalyst path on energy diagram:

4. 2 types of catalysts:

ConcentrationSurface AreaNature of the reactantsTempCatalyst

2. What do catalysts do to speed up a reaction?

3. Draw catalyst path on energy diagram:

4. 2 types of catalysts:

2. What do catalysts do to speed up a reaction?Provide alternate path/lowers activation energy

3. Draw catalyst path on energy diagram: a.e.

4. 2 types of catalysts: RP

Heterogeneous – provides a place for the reaction to occur

Homogeneous – becomes part of the reaction mechanismthen gets spit back out.

5. CaCO3(s) + heat CaO(s) + CO2(g)

a. CaCO3(s) added: __________b. Heat added: __________c. CaO removed: __________d. Pressure increased: __________e. Temp decreased: __________

6. 2H2(g) + O2(g) 2H2O(g) + heat

a. H2 is added: __________b. Heat is added: __________c. O2 is removed: __________d. Pressure is increased: __________e. Temp decreased: __________

a. CaCO3(s) added: productsb. Heat added: productsc. CaO removed: productsd. Pressure increased: reactantse. Temp decreased: products

6. 2H2(g) + O2(g) 2H2O(g) + heat

a. H2 is added: __________b. Heat is added: __________c. O2 is removed: __________d. Pressure is increased: __________e. Temp decreased: __________

a. CaCO3(s) added: productsb. Heat added: productsc. CaO removed: productsd. Pressure increased: reactantse. Temp decreased: reactants

6. 2H2(g) + O2(g) 2H2O(g) + heat

a. H2 is added: productsb. Heat is added: productsc. O2 is removed: reactantsd. Pressure is increased: productse. Temp decreased: products

7. H2(g) + Cl2(g) 2HCl(g) + 93.2kJ

a. H2 is added: __________b. Heat is added: __________c. HCl is removed: __________d. Pressure is increased: __________e. Temp decreased: __________

8. ____CH2(g) + ____ O2(g) ____O2(g) + ___H2O(g) + 890kJ

a. CO2 is added: __________b. Heat is added: __________c. CO2 is removed: __________d. Pressure is increased: __________e. Temp decreased: __________

7. H2(g) + Cl2(g) 2HCl(g) + 93.2kJ

a. H2 is added: productsb. Heat is added: reactantsc. HCl is removed: productsd. Pressure is increased: no effecte. Temp decreased: products

8. ____CH2(g) + ____ O2(g) ____CO2(g) + ___H2O(g) + 890kJ

7. H2(g) + Cl2(g) 2HCl(g) + 93.2kJ

8. 2 CH2(g) + 3 O2(g) 2 CO2(g) + 2 H2O(g) + 890kJ

7. H2(g) + Cl2(g) 2HCl(g) + 93.2kJ

8. 2 CH2(g) + 3 O2(g) 2 CO2(g) + 2 H2O(g) + 890kJ

a. CO2 is added: reactantsb. Heat is added: reactantsc. CO2 is removed: productsd. Pressure is increased: productse. Temp decreased: products

9. Br2(l) + heat Br2(g)

a. Br2(g) is added: __________b. Heat is added: __________c. Br2(g) is removed: __________d. Pressure is decreased: __________e. Temp decreased: __________

10. Lab18.1 Alka-seltzer reaction rates:1. Hot, cold and room temp water affected the rate of reaction, proved:

2. Whole, broken, and powdered tablets affected the rate of reaction, proved:

3. Cork stopper to test tube reaction of vinegar and baking soda proved:

a. Br2(g) is added: reactantsb. Heat is added: productsc. Br2(g) is removed: productsd. Pressure is decreased: productse. Temp decreased: reactants

2. Whole, broken, and powdered tablets affected the rate of reaction, proved:

3. Cork stopper to test tube reaction of vinegar and baking soda proved:

a. Br2(g) is added: reactantsb. Heat is added: productsc. Br2(g) is removed: productsd. Pressure is decreased: productse. Temp decreased: reactants

Higher temp = faster rate

2. Whole, broken, and powdered tablets affected the rate of reaction, proved: more surface area = faster rate

3. Cork stopper to test tube reaction of vinegar and baking soda proved: if products have more moles of gas, the corkcreates greater pressure = slower rate

Ch18 HW#2 7 – 9 7.Can a pressure change be used to shift equilibrium every reversible reaction?

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) + heat

8. Affect equilibrium: C(s) + H2O(g) + heat CO(g) + H2(g)

a) lower tempb) Increase pressurec) Remove H2

d) Add H2Oe) Catalystf) Raise temp and decrease pressure

9. Affect equilibrium: 2SO3(g) + CO2(g) + heat CS2(g) + 4O2(g)

a) Add CO2

b) Add heatc) Decrease pressured)Remove O2

e) Add catalyst

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) + heatNot when there are no gases present, or equal numbers.

a) lower tempb) Increase pressurec) Remove H2

d) Add H2Oe) Catalystf) Raise temp and decrease pressure

a) Add CO2

e) Add catalyst

a) lower temp Reactants b) Increase pressure Reactantsc) Remove H2 Productsd) Add H2Oe) Catalystf) Raise temp and decrease pressure

a) Add CO2

e) Add catalyst

a) lower temp Reactants b) Increase pressure Reactantsc) Remove H2 Productsd) Add H2O Productse) Catalyst No Changef) Raise temp and decrease pressure Both favor products

a) Add CO2

e) Add catalyst

a) Add CO2 Productsb) Add heat Productsc) Decrease pressure Productsd)Remove O2

e) Add catalyst

a) Add CO2 Productsb) Add heat Productsc) Decrease pressure Productsd)Remove O2 Productse) Add catalyst No Change

Ch18.3 – Spontaneous Reactions2 things contribute to deciding if a reaction will proceed on its own:

Free Energy & Entropy

Free Energy – energy released from reactions

Gasoline(g) + O2(g) CO2(g) + H2O(g) + heat

can do work

Exothermic reactions are usually spontaneousEndothermic reactions are usually non spontaneous

- they can be spontaneous if the amount of disorder created has a bigger affect than the increase in energy

Entropy (S) – a measure of the amount of disorder in a system. Natural processes head toward disorder

Natural processes:

Energy: High energy low energy These will oppose each other.

Entropy: Order Disorder One will beat the other

Most Least order orderSolids ↔ Liquids ↔ GasesLeast Most energy energy

Ex) Are the following reactions spontaneous? Predict

a) H2O(l) → H2O(g)

b) C(s) + O2 (g) → CO2(g) + 393.5 kJ

Ex) Are the following reactions spontaneous? Predict

a) H2O(l) → H2O(g) more order → more disorderless energy ← more energy

b) C(s) + O2 (g) → CO2(g) + 393.5 kJ order disorder → disorder

less E more E ← More E (wins)

Ch18 HW#3 10 – 17

Lab18.2 – Equilibrium

- due in 2 days

- Ch18 HW#3 due at beginning of period

Ch18 HW#3 10 – 17 10) Where does “lost” free energy end up?

11) Does free energy that’s lost as waste heat ever serve a useful function?

12) What’s a spontaneous reaction? Ex from life?

13) Products in one spontaneous reactions are more ordered then reactants.Is the entropy change favorable or unfavorable?

14) Higher entropy: a) new pack playing cards or used cardsb) sugar cube dissolved in water or cube?c) 1g salt crystal or 1g powdered.

15) Are all spontaneous reactions exothermic?

10) Where does “lost” free energy end up?waste heat energy

11) Does free energy that’s lost as waste heat ever serve a useful function?

11) Does free energy that’s lost as waste heat ever serve a useful function?Some heat energy can be converted into useful work

12) What’s a spontaneous reaction? Ex from life?A rxn that proceeds forward on its own

Glucose and oxygen react to form carbon dioxide and water in your body13) Products in one spontaneous reactions are more ordered then reactants.

Is the entropy change favorable or unfavorable?reactants products If this rxn is spontaneousless order more order order doesn’t support this!

Therefore entropy is unfavorable(This rxn MUST have a big energy change.)

14) Higher entropy: a) new pack playing cards or used cards Usedb) sugar cube dissolved in water or cube?

Dissolvedc) 1g salt crystal or 1g powdered. Powder

14) Higher entropy: a) new pack playing cards or used cards Usedb) sugar cube dissolved in water or cube?

Dissolvedc) 1g salt crystal or 1g powdered. Powder

15) Are all spontaneous reactions exothermic? Not always,an endothermic rxn can be spont if big increase in entropy.

16) At normal atm pressure, steam condenses to liquid.Is entropy change favorable?

17) Guess

a) CaCO3(s) CaO(s) +CO2(g)

b) 2 H2(g) + O2(g) 2 H2O(l)

c) H2(g) + Cl2(g) 2 HCl(g)

d) CH4(g) + O2(g) CO2(g) + H2O(g)

e)Br2(l) Br2(g)

16) At normal atm pressure, steam condenses to liquid.Is entropy change favorable? No, liquid has more order.

17) Guess

b) 2 H2(g) + O2(g) 2 H2O(l)

c) H2(g) + Cl2(g) 2 HCl(g) + 93.2kJ

d) CH4(g) + O2(g) CO2(g) + H2O(g) + 890kJ

e)Br2(l) Br2(g)

17) Guess

order order disorder (spont) low E low E high E (non-spont)b) 2 H2(g) + O2(g) 2 H2O(l)

c) H2(g) + Cl2(g) 2 HCl(g) + 93.2kJ

d) CH4(g) + O2(g) CO2(g) + H2O(g) + 890kJ

e)Br2(l) Br2(g)

17) Guess

disorder disorder order (non-spont) high E high E lower E (spont)c) H2(g) + Cl2(g) 2 HCl(g) + 93.2kJ

d) CH4(g) + O2(g) CO2(g) + H2O(g) + 890kJ

e)Br2(l) Br2(g)

17) Guess

disorder disorder order (non-spont) high E high E lower E (spont)c) H2(g) + Cl2(g) 2 HCl(g) + 93.2kJ (exothermic) disorder disorder disorder(non-spont) high E high E lower E (spont)d) CH4(g) + O2(g) CO2(g) + H2O(g) + 890kJ

e)Br2(l) Br2(g)

17) Guess

disorder disorder order (non-spont) high E high E lower E (spont)c) H2(g) + Cl2(g) 2 HCl(g) + 93.2kJ (exothermic) disorder disorder disorder(non-spont) high E high E lower E (spont)d) CH4(g) + O2(g) CO2(g) + H2O(g) + 890kJdisorder disorder disorder (no effect) high E high E high E high E exothermic (spont)e)Br2(l) Br2(g)

17) Guess

disorder disorder order (non-spont) high E high E lower E (spont)c) H2(g) + Cl2(g) 2 HCl(g) + 93.2kJ (exothermic) disorder disorder disorder(non-spont) high E high E lower E (spont)d) CH4(g) + O2(g) CO2(g) + H2O(g) + 890kJdisorder disorder disorder (no effect) high E high E high E high E exothermic (spont)e)Br2(l) Br2(g) order disorder (spont) low E high E (non-spont)

Ch18.4 – Equilibrium Constants

Balance: H2(g) + I2(g) HI(g)

H2(g) + I2(g) 2HI(g)

At equilibrium: 2% 98%

Chemists don’t use % to indicate the position of equilibrium, instead use molarity and ratios.

H2(g) + I2(g) 2HI(g)

At equilibrium: 2% 98%

Chemists don’t use % to indicate the position of equilibrium, instead use molarity and ratios.

Keq – equilibrium constant

- compares the rate of reverse reaction to rate of forward

The brackets represent molarity. Each substance’s molarity is raised to the power of the reaction coefficient.

Ex1) Write Keq for H2(g) + I2(g) 2HI(g)

]reactants[

]products[eqK

Ex 2) At 10oC, a 1 liter container has 0.0045 mol N2O4 in equilibrium with 0.030 mol NO2

a) Write an equation:

b) Write Keq:

c) Calc Keq:

Ex 2) At 10oC, a 1 liter container has 0.0045 mol N2O4 in equilibrium with 0.030 mol NO2

a) Write an equation: N2O4 2NO2

b) Write Keq:

c) Calc Keq:

Keq is unique for every reaction, and for every temp. If temp goes up, usually Keq goes up.

Keq > 1 products favored

Keq < 1 reactants favored

OKeq 2.0

]0045.0[

]03.0[ 2

Ex 3) At a certain temp, 0.500M H2, 0.500M N2 are in equilibrium with 2.500M NH3. Calc Keq

Ex 4) Given Keq = 100, [NH3] = 1.25M, [H2] = 1.75M, Find [N2]

Ch18 HW#4 WS

Ch18 HW#4 1. Write the equilibrium expression for the oxidation of hydrogen to form water vapor.

2H2(g) + O2(g) 2H2O(g)

2. Write the equilibrium expression for the formation of nitrosyl bromide.

2NO(g) + Br2(g) 2NOBr(g)

3. Write the equilibrium expression for the following reaction

NO(g) + O3(g) O2(g) + NO2(g)

2H2(g) + O2(g) 2H2O(g)

NO(g) + O3(g) O2(g) + NO2(g)

2H2(g) + O2(g) 2H2O(g)

NO(g) + O3(g) O2(g) + NO2(g)

NOBrKeq

2H2(g) + O2(g) 2H2O(g)

NO(g) + O3(g) O2(g) + NO2(g)

NOBrKeq

ONOKeq

CH4(g) + CI2(g) CH3CI(g) + HCI(g)

CH4(g) + H20(g) CO(g) + 3H2(g)

CO(g) + 2H2(g) CH3OH(g)

7. Same: