1. The graph below shows the concentration of Br2 as a function of time for the reaction

H2(g) + Br2(g) → 2 HBr(g). What is the average rate of the reaction between 20 s and

80 s?

A. 0.040 M/s C. 0.033M/s

B. 0.0067 M/s D. 0.010 M/s

2. The reaction 2 NO2(g) + Cl2(g) → 2 NO2Cl(g) has the rate law

Rate = k[NO2][Cl]

When Δ[Cl2]/Δt = 0.10 M/s, what is Δ[NO2Cl]/Δt?

A. 0.20 M/s C. 0.10 M/s

B. 0.20 M/s D. 0.050 M/s

3. The reaction NO2(g) + CO(g) → NO(g) + CO2(g) was found to be second order in NO2

and zero order in CO. What is the effect on the rate when the concentrations of NO2 and

CO are both tripled?

A. The rate increases by a factor of 9. C. The rate increases by a factor of 27.

B. The rate increases by a factor of 36. D. The rate increases by a factor of 12.

4. Which statement must be true about this reaction?

I(aq) + I2(aq) → I3

(aq)

A. The rate law is: rate = k[I][I2].

B. If the reaction is an elementary step, the rate law is: rate = k[I][I2].

C. The reaction is catalyzed by I.

D. Δ[I3]/Δt = (Δ[I

]/Δt + Δ[I2]/Δt)

5. The reaction

2 H2(g) + 2 NO(g) → 2 H2O(g) + N2(g)

follows the rate law

Rate = k[H2][NO ]2

What is the overall kinetic order of the reaction?

A. first order

B. second order

C. third order

D. fourth order

6. The initial rate of the reaction 2 ClO2(aq) + 2 OH− → ClO3

−(aq) + ClO2

−(aq) + H2O(l)

was measured at several different concentrations of the reactants with the following

results.

experiment [ClO2] (M) [OH−] (M) Rate (M/s)

1 0.060 0.030 0.0248

2 0.020 0.030 0.00276

3 0.020 0.090 0.00828

What is the experimental rate law for the reaction?

A. rate = k[ClO2][OH−] C. rate = k[ClO2]

2[OH

−]

B. rate = k[ClO2][OH−]

2 D. rate = k[ClO2]

2[OH

−]

2

7. According to the plot below, which of these reactions demonstrates first-order kinetics?

A. Reaction 1 C. Reaction 3

B. Reaction 2 D. Reaction 4

8. Radioactive iodine-137 has a half-life of 24.13 s. How much of a 75.0 g sample of 137

I is

left after 77.0 s? Radioactive decay follows first-order kinetics.

A. 0.625 g C. 8.22 g

B. 10.2 g D. 5.25 g

9. The plot below shows the progress of the reaction SO2Cl2(g) → SO2(g) + Cl2(g) as a

function of time. What is the rate law of the reaction?

A. Rate = 3.75 × 104

M·s1

C. Rate = (3.75 × 104

s1

)[SO2Cl2]

B. Rate = (2.67 × 103 M

1·s1

)[SO2Cl2]2 D. Rate = (2.67 × 10

3 s1

)[SO2Cl2]

10. The equation below was determined to be the best fit to a straight line for the Arrhenius

plot of first-order reaction. What is the activation energy of the reaction?

y = −11283x + 28.964

A. 343.3 kJ/mol C. 135.7 kJ/mol

B. 112.8 kJ/mol D. 93.81 kJ/mol

11. Given the following proposed mechanism, predict the rate law for the overall reaction.

2 NO2(g) + Cl2(g) → 2 NO2Cl(g) overall reaction

Mechanism

NO2 + Cl2 → NO2Cl + Cl slow

NO2 + Cl → NO2Cl fast

A. Rate = k[NO2][Cl2] C. Rate = k[NO2Cl][Cl]

B. Rate = k[NO2]2[Cl2] D. Rate = k[NO2][Cl]

12. The following mechanism has been proposed for a reaction that occurs in aqueous

solution.

Ce4+

(aq) + Mn2+

(aq) → Ce3+

(aq) + Mn3+

(aq)

Ce4+

(aq) + Mn3+

(aq) → Ce3+

(aq) + Mn4+

(aq)

Mn4+

(aq) + Tl+ (aq) → Tl

3+(aq) + Mn

2+(aq)

Which one of the following is a reaction intermediate for the reaction?

A. Mn3+

(aq) C. Ce3+

(aq)

B. Tl3+

(aq) D. Mn2+

(aq)

13. Which statement is correct?

A. A catalyst accelerates a reaction by lowering Ea for the forward reaction but not the

reverse reaction.

B. A homogeneous catalyst is in the same phase as the reactants.

C. A catalyst increases the equilibrium concentrations of products and decreases the

equilibrium concentrations of reactants.

D. Biological catalysts are called substrates.

14. A reversible reaction was found to have an activation energy in the forward direction of

145.0 kJ/mol and ΔHrxn = 69.0 kJ/mol. What is the activation energy for the reverse

reaction?

A. 145 kJ/mol C. 76.0 kJ/mol

B. 69.0 kJ/mol D. 214 kJ/mol

15. Which one of the following is the equilibrium constant, Kc, for the reaction below?

C(s) + 2 H2(g) ⇌ CH4(g)

A. [CH4 ]

[C][H2 ]2 C. [CH4 ]

[H2 ]2

B. [CH4 ]

[C]

D.

CH4[ ] H2[ ]2

16. CaCO3(s) is placed in a closed container with 0.25 atm of 14

CO2(g). 14

C is a long-lived

radioactive isotope of carbon. At 1000 K, KP = 3.9 × 102

for this reaction.

CaCO3(s) ⇌ CaO(s) + CO2(g)

After a long period of time at 1000 K, radioactive 14

C will be found in

A. CaCO3(s) and CO2(g) C. CaCO3(s) only

B. CO2(g) only D. CaCO3(s), CO(g) and CO2(g)

17. At 700 K

Kp = 54.0 for H2(g) + I2(g) ⇌ 2 HI(g)

and Kp = 1.04 × 10−4

for N2(g) + 3 H2(g) ⇌ 2 NH3(g)

What is Kp for 2 NH3(g) + 3 I2(g) ⇌ 6 HI(g) + N2(g) at 700 K?

A. 5.00 × 109 C. 1.51 × 10

9

B. 1.54 × 10−4

D. 1.60 × 10−6

18. What is KP at 1273 °C for this reaction?

2 CO2(g) ⇌ 2 CO(g) + O2(g)

KC = 4.46 × 1023

at the same temperature.

A. 5.65 × 1021

C. 4.46 × 1023

B. 1.77 × 1020

D. 4.66 × 1021

19. At 298 K the Kp for the reaction below is 0.0817. The reaction starts with a mixture of

NO, Br2, and NOBr at pressures 1.00 atm, 5.00atm, and 1.00 atm respectively. Which one

of the following is true after the reaction has reached equilibrium at 298 K?

2 NO(g) + Br2(g) ⇌ 2 NOBr(g)

A. At equilibrium the total pressure will be greater than the initial total pressure (7.00

atm).

B. At equilibrium the total pressure will be equal to the initial total pressure (7.00 atm).

C. At equilibrium the total pressure will be less than the initial total pressure (7.00 atm).

D. At equilibrium the total pressure will be 1/3 of the initial total pressure (7.00 atm).

20. What is [H2] at equilibrium when [O2] = 0.012 M, [H2O] = 0.045 M and KC = 3.0 × 103?

2 H2(g) + O2(g) ⇌ 2 H2O(g)

A. 4.8 × 105

M C. 2.3 × 109

M

B. 7.5 × 103

M D. 6.3 × 102

M

21. A 0.0500 mol sample of NO2(g) is placed in a 1.00 L reaction vessel containing no N2O4.

At equilibrium the vessel contained 0.0150 mol of N2O4(g). What is Kc for the reaction

below?

2 NO2(g) ⇌ N2O4(g)

A. 37.5 C. 6.00

B. 62.5 D. 7.50

22. KP = 4.6 × 107

at 730 °C for the reaction:

2 HBr(g) ⇌ H2(g) + Br2(g)

Starting with 2.0 atm of HBr in a 1.0-L reaction vessel, calculate the equilibrium pressure

of H2.

A. 2.0 × 106

atm C. 6.7 × 104

atm

B. 9.6 × 104

atm D. 1.4 × 103

atm

23. Consider the following reaction at equilibrium.

N2(g) + 3 H2(g) ⇌ 2 NH3(g)

Which of the following will increase the amount of NH3(g) in the reaction vessel at

constant temperature?

A. an increase in the total pressure in the container by adding helium at constant

volume.

B. a decrease in the partial pressure of N2.

C. an increase in total volume of the reaction vessel.

D. an increase in the total pressure.

24. Which change will cause this reaction at equilibrium to shift to the right (in the direction

of products)?

CuS(s) + O2(g) ⇌ Cu(s) + SO2(g) ΔH° = 244 kJ/mol

A. Reducing the volume of the reaction mixture

B. Increasing the amount of CuS(s) present

C. Decreasing the temperature

D. Adding SO2(g) to the system

25. What is the conjugate base of H2AsO3−?

A. H3AsO3 C. HAsO32−

B. H2AsO3− D. AsO3

3−

26. What is the concentration of hydroxide ion in pure water at 30.0 °C?

Kw = 1.47 × 1014 at 30.0 °C

A. 1.47 × 1014

M C. 1.21 × 107

M

B. 1.00 × 107

M D. 1.21 × 106

M

27. An aqueous solution with pOH = 4.15 at 25 °C also has

A. pH = 7.85 C. Kw = 1.00 × 107

B. [OH] = 7.08 × 10

5 M D. [H3O

+] = 1.41 × 10

4 M

28. Which of the following statements is true for a 0.0010 M aqueous HCN solution?

A. pH = 3.0 C. [HCN] < [H3O+]

B. [H3O+] = [CN

] D. [OH

] > [H3O

+]

29. A 0.050 M aqueous solution of C7H7NH3+ Cl

has pH = 3.60 at 25 °C. C7H7NH3

+ Cl

is a

A. weak acid C. strong acid

B. weak base D. strong base

30. Ka of hypochlorous acid, HClO, is 2.0 × 10−8

. Which one of the following is false for this

reaction at equilibrium?

HClO(aq) ⇌ H+(aq) + ClO

-(aq)

A. The rate constant of the forward reaction is smaller than the rate constant of the

reverse reaction.

B. HClO is only partially ionized in aqueous solution.

C. The rate of the reaction in the forward direction is smaller than the rate of the

reaction in the reverse direction.

D. The forward reaction does not proceed very far.

CHE 107 FALL 2012 Exam 2 Key

1. B

2. B

3. A

4. B

5. C

6. C

7. C

8. C

9. C

10. D

11. A

12. A

13. B

14. C

15. C

16. A

17. C

18. A

19. A

20. B

21. A

22. D

23. D

24. C

25. C

26. C

27. B

28. B

29. A

30. C