Practice Exam 2
This exam is provided for you to have extra practice. There is no guarantee that it represents all (or any) problems
that will be on your actual exam.
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. Which of the following expressions relates the rates of reaction of NOCl(g) and Cl2(g)?
2 NOCl(g)  2 NO(g) + Cl2(g)
a.
=
b.
-2
=
c.
=
d.
=
e.
=
____
2. Given the initial rate data for the decomposition reaction,
AB+C
determine the rate expression for the reaction.
[A], M
0.110
0.220
0.330
a.
b.
c.
d.
e.
____
-[A]/t M/s
7.81  10-3
3.12  10-2
7.03  10-2
= 7.10  10-2s-1[A]
= 0.645 M-1s-1[A]2
= 3.63  10-2M-1s-1[A]2
= 3.63  10-2M s-1
= 5.87 M-2s-1[A]3
3. Given the initial rate data for the reaction A + B  C, determine the rate expression for the reaction.
[A], M
0.250
0.250
0.500
a.
b.
c.
d.
e.
____
[B], M
0.150
0.300
0.300
[C]/t (initial) M/s
8.90  10-6
1.78  10-5
7.12  10-5
= 2.37  10-4 M-1s-1 [A][B]
= 9.49  10-4 M-2s-1 [A]2[B]
= 1.58  10-3 M-2s-1 [A][B]2
= 6.33  10-3 M-3s-1 [A]2[B]2
= 3.80  10-3 M-3s-1 [A]3[B]
4. The reaction of NO and O2 produces NO2.
2 NO(g) + O2(g)  2 NO2(g)
The reaction is second-order with respect to NO(g) and first-order with respect to O2(g). At a given temperature,
the rate constant, k, equals 6.1  103 M-2s-1. What is the rate of reaction when the initial concentrations of NO
and O2 are 0.020 M and 0.015 M, respectively?
a. 9.8  10-10 M/s
b. 0.027 M/s
c. 0.037 M/s
d. 1.0 M/s
e. 1.8 M/s
____
5. A student analyzed a first-order reaction and obtained the graph below. Unfortunately, the student forgot to
label the axes. What are the correct labels for the x and y axes?
a.
b.
c.
d.
e.
____
x axis = time, y axis = ln[A]
x axis = time, y axis = [A]
x axis = time, y axis = 1/[A]
x axis = 1/Time, y axis = [A]
x axis = 1/Time, y axis = 1/[A]
6. What is the rate constant for a first-order reaction if the half-life of the reaction is 6.43  10-5 seconds?
a. 9.28  10-5 s-1
b. 0.0967 s-1
c. 10.3 s-1
d. 1.08  104 s-1
e. 1.56  104 s-1
____
7. For the first-order decomposition of N2O5 at 340 K, where k = 5.8  10-3 s-1, calculate the original concentration
if the concentration of N2O5 is 0.41 M after 209 seconds.
a. 0.12 M
b. 0.23 M
c. 0.72 M
d. 1.4 M
e. 1.7 M
____
8. The decomposition of formic acid follows first-order kinetics.
HCO2H(g)  CO2(g) + H2(g)
The half-life for the reaction at 550 C is 24 seconds. How many seconds does it take for the formic acid
concentration to decrease by 75%?
a. 6.0 s
b. 18 s
c. 24 s
d. 36 s
e. 48 s
____
9. Calculate the activation energy, Ea for
N2O5(g)  2 NO2(g) +
O2(g)
given k (at 25.0 °C) = 3.46  10-5 s-1 and k (at 45.0 C) = 5.79  10-4 s-1. (R = 8.314 J/K·mol)
a. 1.32 kJ/mol
b. 1.61 kJ/mol
c. 14.0 kJ/mol
d. 48.2 kJ/mol
e. 111 kJ/mol
____ 10. Nitrogen dioxide reacts with carbon monoxide to produce nitrogen monoxide and carbon dioxide.
NO2(g) + CO(g)  NO(g) + CO2(g)
A proposed mechanism for this reaction is
2 NO2(g)↔ NO3(g) + NO(g) (fast, equilibrium)
NO3(g) + CO(g)  NO2(g) + CO2(g) (slow)
What is a rate law that is consistent with the proposed mechanism?
a. rate = k[NO2][CO]
b. rate = k[[NO2]2[CO]
c. rate = k[[NO2]2[CO]/[NO]
d. rate = k[NO3][CO]
e. rate = k[NO2]2
____ 11. Write the expression for K for the reaction below.
Al2S3(s) ↔ 2 Al3+(aq) + 3 S2-(aq)
a. K = [Al3+]2[S2-]3
b. K = [Al3+][S2-]
c. K = [2 Al3+][3 S2-]
d.
K=
e.
K=
____ 12. What is the relationship between Kp and Kc for the reaction below?
CS2(g) + 3 Cl2(g) ↔ S2Cl2(g) + CCl4(g)
a.
Kc =
b.
Kc =
c. Kc = (RT)2Kp
d.
Kc =
e.
Kc =
____ 13. The reaction below is studied at a high temperature.
PCl5(g) ↔ PCl3(g) + Cl2(g)
At equilibrium, the partial pressures of the gases are as follows: PCl5 = 1.8  10-2 atm, PCl3 = 5.6  10-2 atm, and
Cl2 = 3.8  10-4 atm. What is the value of Kp for the reaction?
a. 3.8  10-7
b. 1.2  10-3
c. 3.1
d. 8.5  102
e. 2.6  106
____ 14. At 25 C, only 1.9 g CaSO4 will dissolve in 2.00 L of water. What is the equilibrium constant for the reaction
below?
CaSO4(s) ↔ Ca2+(aq) + SO42-(aq)
a. 4.9  10-5
b. 1.9  10-4
c. 1.4  10-2
d. 7.0 10-3
e. 0.90
____ 15. We place 0.0774 mol N2O4(g) in a 1.00 L flask at a given temperature. After reaching equilibrium, the
concentration of NO2(g) is 0.0068 M. What is Kc for the reaction below?
N2O4(g) ↔2 NO2(g)
a.
b.
c.
d.
e.
8.8  10-5
5.9  10-4
6.2  10-4
7.2 10-4
9.6  10-2
____ 16. A mixture of 0.200 mol NO2 and 0.200 mol CO is placed in a 1.00 L flask and given time to equilibrate.
Analysis of the equilibrium mixture indicates that 0.134 mol of CO2 is present. Calculate Kc for the reaction.
NO2(g) + CO(g) ↔NO(g) + CO2(g)
a.
b.
c.
d.
e.
0.27
0.45
0.67
2.0
4.1
____ 17. At 2010 K, the equilibrium constant, Kc, for the following reaction is 4.0  10-4.
N2(g) + O2(g) ↔2 NO(g)
If the equilibrium concentrations of N2 and O2 are 0.28 mol/L and 0.38 mol/L at 2010 K, what is the equilibrium
concentration of NO?
a. 1.8  10-9 M
b. 2.1  10-5 M
c. 4.3  10-5 M
d. 6.5  10-3 M
e. 6.1  10-2 M
____ 18. We place 1.32 mol PCl5 in a 1.0 L flask and allow it to reach equilibrium at a given temperature. What is the
final concentration of Cl2 in the flask?
PCl5(g) ↔PCl3(aq) + Cl2(g) Kc = 0.47
a.
b.
c.
d.
e.
0.36 M
0.59 M
0.62 M
0.79 M
85 M
____ 19. For the following reaction,
2 SO2(g) + O2(g) ↔2 SO3(g)
the equilibrium constant, Kp, is 0.758 at 627 C. What is the equilibrium constant, at 627 C, for the reaction
below?
SO3(g) ↔SO2(g) + 1/2 O2(g)
a.
b.
c.
d.
e.
0.660
0.871
1.15
1.32
1.74
____ 20. Assume that the following endothermic chemical reaction is at equilibrium.
C(s) + H2O(g) ↔H2(g) + CO(g)
Which of the following statements are CORRECT?
1. Increasing the amount of C(s) will increase the equilibrium concentration of CO(g).
2. Increasing the temperature will increase the equilibrium concentration of H2(g).
3. Decreasing the concentration of H2O(g) will increase the equilibrium concentration of CO(g).
a.
b.
c.
d.
e.
1 only
2 only
3 only
1 and 2
1, 2, and 3
Exam 2
Answer Section
MULTIPLE CHOICE
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A
PTS: 1
OBJ: 15.1 Rates of Chemical Reactions
B
PTS: 1
OBJ: 15.3 Effect of Concentration on Reaction Rate
B
PTS: 1
OBJ: 15.3 Effect of Concentration on Reaction Rate
C
PTS: 1
OBJ: 15.3 Effect of Concentration on Reaction Rate
A
PTS: 1
15.4 Concentration-Time Relationships: Integrated Rate Laws
D
PTS: 1
15.4 Concentration-Time Relationships: Integrated Rate Laws
D
PTS: 1
15.4 Concentration-Time Relationships: Integrated Rate Laws
E
PTS: 1
15.4 Concentration-Time Relationships: Integrated Rate Laws
E
PTS: 1
OBJ: 15.5 A Microscopic View of Reaction Rates
C
PTS: 1
OBJ: 15.6 Reaction Mechanisms
A
PTS: 1
OBJ: 16.2 The Equilibrium Constant and the Reaction Quotient
C
PTS: 1
OBJ: 16.2 The Equilibrium Constant and the Reaction Quotient
B
PTS: 1
OBJ: 16.3 Determining an Equilibrium Constant
A
PTS: 1
OBJ: 16.3 Determining an Equilibrium Constant
C
PTS: 1
OBJ: 16.3 Determining an Equilibrium Constant
E
PTS: 1
OBJ: 16.3 Determining an Equilibrium Constant
D
PTS: 1
OBJ: 16.4 Using Equilibrium Constants in Calculations
B
PTS: 1
OBJ: 16.4 Using Equilibrium Constants in Calculations
C
PTS: 1
16.5 More about Balanced Equations and Equilibrium Constants
B
PTS: 1
16.5 More about Balanced Equations and Equilibrium Constants