Ch 15 Practice Problems
Chem 1B
1. The average rate of disappearance of ozone in the reaction 2O3(g)  3O2(g) is found to be 8.9  10–3 atm over a
certain interval of time. What is the rate of appearance of O 2 during this interval?
A) 1.3  10–2 atm/time
B) 8.9  10–3 atm/time
C) 5.9  10–3 atm/time
D) 2.7  10–2 atm/time
E)
1.8  10–2 atm/time
2. The rate constant k is dependent on
A) the concentration of the reactant.
B) the concentration of the product.
C) the temperature.
D) the order of the reaction.
E)
none of these
3. The rate expression for a particular reaction is Rate = k[A][B]2. If the initial concentration of B is increased from
0.1 M to 0.3 M, the initial rate will increase by which of the following factors?
A) 3
B) 27
C) 4
D) 6
E)
9
4. A first-order reaction is 43% complete at the end of 18 min. What is the value of the rate constant?
A)
B)
C)
D)
E)
3.1 x 10-2 min-1
0.21 min-1
0.031 min-1
4.7  10-2 min-1
1.4  10-2 min-1
Use the following to answer questions 5-10:
A general reaction written as 2A + 2B  C + 2D is studied and yields the following data.
5.
[A]0
[B]0
Initial [C]/t
0.100 M
0.100 M
4.00  10–5 mol/L • s
0.200 M
0.100 M
4.00  10–5 mol/L • s
0.100 M
0.200 M
8.00  10–5 mol/L • s
For the first of the reactions in the table of data, determine -[B]/t.
A) 4.00  10–5
B) 8.00  10–5
C) 1.60  10–4
D) 2.00  10–5
E)
none of these
6.
7.
What is the order of the reaction with respect to B?
A) 1
B) 4
C) 3
D) 2
E)
0
What is the order of the reaction with respect to A?
A) 1
B) 4
C) 3
D) 2
E)
0
8. What is the overall order of the reaction?
A) 1
B) 4
C) 3
D) 2
E)
0
9. What are the proper units for the rate constant for the reaction?
A) s–1
B) mol L–1 s–1
C) L mol–1 s–1
D) L3 mol–3 s–1
E)
L2 mol–2 s–1
10. What is the numerical value of the rate constant?
A) 4.00  10–4
B) 4.00  10–3
C) 4.00  10–2
D) 4.00  10–1
E)
none of these
11. Use the following initial rate data for the reaction in aqueous solution to determine the rate law.
[Br2 ]
(M/s)
t
+
[CH3COCH3]0 (M)
[Br2]0 (M)
[H ]0 (M)
A)
B)
C)
D)
E)
1.00
1.00
1.00
4.0  10–3
2.00
1.00
1.00
8.0  10–3
2.00
2.00
1.00
8.0  10–3
1.00
2.00
2.00
8.0  10–3
Rate = k[Br2][H+]
Rate = k[CH3COCH3][Br2]
Rate = k[CH3COCH3][H+]
Rate = k[CH3COCH3][Br2][H+]
Rate = k[CH3COCH3][Br2][H+]2
12. The reaction of (CH3)3CBr with hydroxide ion proceeds with the formation of (CH3)3COH.
(CH3)3CBr (aq) + OH– (aq)  (CH3)3COH (aq) + Br– (aq)
The following data were obtained at 55°C.
[(CH3)3CBr]0
[HO–]0
Initial Rate
Exp.
(mol/L)
(mol/L)
(mol/L • s)
1
0.10
0.10
1.0  10–3
2
0.20
0.10
2.0  10–3
3
0.10
0.20
1.0  10–3
4
0.30
0.20
?
What will the initial rate (in mol/L • s) be in Experiment 4?
A)
B)
C)
D)
E)
3.0  10–3
6.0  10–3
9.0  10–3
18  10–3
none of these
13. For which order reaction is the half-life of the reaction independent of the initial concentration of the reactant(s)?
A) zero order
B) first order
C) second order
D) all of these
E)
none of these
14. The OH radical disproportionates according to the elementary chemical reaction OH + OH  H2O + O. This
reaction is second order in OH. The rate constant for the reaction is 2.4  10–12 cm3/molecule • s at room
temperature. If the initial OH concentration is 1.7  1013 molecules/cm3, what is the first half-life for the
reaction?
A) 3.5  1024 s
B) 2.9  1011 s
C) 0.025 s
D) 4.9 s
E)
4.2 s
15. The reaction A  B + C is known to be zero order in A with a rate constant of 3.8  10–2 mol/L • s at 25° C. An
experiment was run at 25°C where [A]0 = 1.8  10–3 M. What is the rate after 6.7 minutes?
A) 3.8  10–2 mol/L • s
B) 1.5  10–11 mol/L • s
C) 6.7  10–4 mol/L • s
D) 1.8  10–3 mol/L • s
E)
6.8  10–5 mol/L • s
16. If the reaction 2HI  H2 + I2 is second order, which of the following will yield a linear plot?
A) log [HI] vs. time
B) 1/[HI] vs. time
C) [HI] vs. time
D) ln [HI] vs. time
Use the following to answer questions 17-20:
For the reaction a A  products, select the reaction order(s) that best fit(s) the observations.
17.
A)
B)
C)
D)
E)
The half-life is constant.
zero order in A
first order in A
second order in A
all of these
none of these
18.
[A] is constant.
A) zero order in A
B) first order in A
C) second order in A
D) all of these
E)
none of these
19.
The rate is constant over time.
A) zero order in A
B) first order in A
C) second order in A
D) all of these
E)
none of these
20.
The half-life decreases over time.
A) zero order in A
B) first order in A
C) second order in A
D) all of these
E)
none of these
21. The reaction A  B + C is known to be zero order in A with a rate constant of 3.6  10–2 mol/L • s at 25° C. An
experiment was run at 25°C where [A]0 = 3.4  10–3 M. What is the half-life for the reaction?
A) 4.7  10–2 s
B) 1.9  101 s
C) 1.8  10–2 s
D) 8.2  104 s
E)
6.1  10–2 s
22. For which order reaction is the half-life of the reaction proportional to 1/k (k is the rate constant)?
A) zero order
B) first order
C) second order
D) all of these
E)
none of these
Use the following to answer questions 23-24:
For a reaction aA  products, [A]0 = 4.0 M, and the first three successive half-lives are 48, 96, and 192 min.
23.
Calculate k (without units).
A) 5.2  10-3
B) 2.6  10-3
C) 4.1  10-3
D) 1.4  10-2
E)
none of these
24.
Calculate [A] at t = 81 min.
A) 1.3 M
B) 1.5 M
C) 2.6 M
D) 3.0 M
E)
none of these
25. The reaction A  B + C is known to be zero order in A with a rate constant of 4.8  10–2 mol/L • s at 25° C. An
experiment was run at 25°C where [A]0 = 2.2 M. What is the concentration of B after 6.0 s?
A) 8.5  10–1 M
B) 1.9 M
C) 1.1  10–1 M
D) 2.9  10–1 M
E)
2.2 M
26. At a particular temperature, N2O5 decomposes according to a first-order rate law with a half-life of 3.0 s. If the
initial concentration of N2O5 is 1.0  1016 molecules/cm3, what will be the concentration in molecules/cm3
after 10.0 s?
A) 9.9  1014
B) 1.8  1012
C) 7.3  109
D) 6.3  103
E)
9.4  102
Use the following to answer questions 27-28:
The following questions refer to the gas-phase decomposition of chloroethane:
C2H5Cl products
Experiment shows that the decomposition is first order. The following data show kinetics information for this
reaction.
Time (s)
ln [C2H5Cl] (M)
1.0
-1.625
2.0
-1.735
27.
What was the initial concentration of the ethylene chloride?
A) 0.29 M
B) 0.35 M
C) 0.11 M
D) 0.02 M
E)
0.22 M
28.
What would the concentration be after 5.0 s?
A) 0.13 M
B) 0.08 M
C) 0.02 M
D) 0.19 M
E)
0.12 M
29. The reaction 2NO2  2NO + O2 obeys the rate law
 O2 
= 1.40  10–2 [NO2]2 at 500° K.
t
If the initial concentration of NO2 is 1.00 M, how long will it take for the [NO2] to decrease to 25.0% of its
initial value?
A)
B)
C)
D)
E)
49.5 s
71.4 s
214 s
1.40  10–2 s
cannot be determined from these data
30. The reaction
2A + B  C
Step 1: A + B
has the following proposed mechanism.
D (fast equilibrium)
Step 2:
D+BE
Step 3:
E+AC+B
If step 2 is the rate-determining step, what should be the rate of formation of C?
A)
B)
C)
D)
E)
k[A]
k[A]2[B]
k[A]2[B]2
k[A][B]
k[A][B]2
31. When ethyl chloride, CH3CH2Cl, is dissolved in 1.0 M NaOH, it is converted into ethanol, CH3CH2OH, by the
reaction
CH3CH2Cl + OH–  CH3CH2OH + Cl–
At 25°C the reaction is first order in CH3CH2Cl, and the rate constant is 1.0  10–3 s–1. If the activation
parameters are A = 3.4  1014 s–1 and Ea = 100.0 kJ/mol, what will the rate constant be at 28°C? (R = 8.314
J/mol • K)
A)
B)
C)
D)
E)
1.5  10–3 s–1
8.9  102 s–1
1.1  10–3 s–1
9.2 10–3 s–1
3.8  1014 s–1
32. The rate law for a reaction is found to be Rate = k[A]2[B]. Which of the following mechanisms gives this rate
law?
I.
A+B
E (fast)
E + B  C + D (slow)
II.
A+B
E (fast)
E + A  C + D (slow)
III.
A + A  E (slow)
E + B  C + D (fast)
A)
B)
C)
D)
E)
I only
II only
III
two of these
none of these
33. The experimental rate law for the decomposition of nitrous oxide (N 2O) to N2 and O2 is Rate = k[N2O]2. Two
mechanisms are proposed:
I. N2O  N2 + O
N2O + O  N2 + O2
II.
2N2O
N4O2
N4O2  2N2 + O2
Which of the following could be a correct mechanism?
A)
B)
C)
D)
E)
Mechanism I with the first step as the rate-determining step.
Mechanism I with the second step as the rate-determining step.
Mechanism II with the second step as the rate-determining step.
Two of these could be correct.
None of these could be correct.
34. The rate constant for a reaction increases from 10.0 s-1 to 100. s-1 when the temperature is increased from 317 K
to 427 K. What is the activation energy for the reaction in kJ/mol? (R = 8.314 J/mol • K)
A) 23.6 kJ/mol
B) 10.2 kJ/mol
C) 1.74 kJ/mol
D) 21.1 kJ/mol
E)
0.0756 kJ/mol
35. The activation energy for the reaction H2(g) + I2(g)  2HI(g) is changed from 184 kJ/mol to 59.0 kJ/mol at 600.
K by the introduction of a Pt catalyst. Calculate the value of the ratio rate(catalyzed)/rate(uncatalyzed).
A) 1.00
B) 7.62  1010
C) 1.38
D) 0.321
E)
none of these
36.
The reaction 2H2O2  2H2O + O2 has the following mechanism:
H2O2 + I–  H2O + IO–
H2O + IO–  H2O + O2 + I–
What is the catalyst in the reaction?
A)
B)
C)
D)
H2O
I–
H2O2
IO–
Answers:
1. A
2. C
3.E
4. A
5. B
6. A
7. E
8. A
9. A
10. A
11. C
12. A
13. B
14. C
15. A
16. B
17. B
18. E
19. A
20. A
21. A
22. D
23. A
24. B
25. D
26. A
27. E
28. A
29. C
30. E
31. A
32. B
33. C
34. A
35. B
36. B