Chapter 16: Kinetics: Rates and Mechanisms of Chemical
Reactions
1. The compound RX3 decomposes according to the equation
3RX3 → R + R2X3 + 3X2
In an experiment the following data were collected for the decomposition at 100°C. What is the
average rate of reaction over the entire experiment?
t(s) [RX3](mol L–1)
0 0.85
2 0.67
6 0.41
8 0.33
12 0.20
14 0.16
A) 0.011 mol L–1s–1 D) 0.049 mol L–1s–1
B) 0.019 mol L–1s–1 E) 0.069 mol L–1s–1
C) 0.044 mol L–1s–1
2. Consider the following reaction
8A(g) + 5B(g) → 8C(g) + 6D(g)
If [C] is increasing at the rate of 4.0 mol L–1s–1, at what rate is [B] changing?
A) –0.40 mol L–1s–1
B) –2.5 mol L–1s–1
C) –4.0 mol L–1s–1
D) –6.4 mol L–1s–1
E) none of the above, since its rate of change must be positive
3. Consider the general reaction
5Br–(aq) + BrO3–(aq) + 6H+(aq) → 3Br2(aq) + 3H2O(aq)
For this reaction, the rate when expressed as [Br2]/t is the same as
A) –[H2O]/t D) –0.6[Br–]/t
B) 3[BrO3–]/t E) none of the above
C) –5[Br–]/t
Chapter 16: Kinetics: Rates and Mechanisms of Chemical Reactions
4. Consider the reaction
2NH3(g) → N2(g) + 3H2(g)
If the rate [H2]/t is 0.030 mol L–1 s–1, then [NH3]/t is
A) –0.045 mol L–1 s–1 D) –0.010 mol L–1 s–1
B) –0.030 mol L–1 s–1 E) none of the above
C) –0.020 mol L–1 s–1
5. For the reaction
3A(g) + 2B(g) → 2C(g) + 2D(g)
the following data were collected at constant temperature. Determine the correct rate law for this
reaction.
Trial Initial [A] Initial [B] Initial Rate
(mol/L) (mol/L) (mol/(L·min))
1 0.200 0.100 6.00 × 10–2
2 0.100 0.100 1.50 × 10–2
3 0.200 0.200 1.20 × 10–1
4 0.300 0.200 2.70 × 10–1
A) Rate = k[A][B] D) Rate = k[A]1.5[B]
B) Rate = k[A][B]2 E) Rate = k[A]2[B]
C) Rate = k[A]3[B]2
6. For the reaction
A(g) + 2B(g) → 2C(g) + 2D(g)
the following data were collected at constant temperature. Determine the correct rate law for this
reaction.
Trial Initial [A] Initial [B] Initial Rate
(mol/L) (mol/L) (mol/(L·min))
1 0.125 0.200 7.25
2 0.375 0.200 21.75
3 0.250 0.400 14.50
4 0.375 0.400 21.75
A) Rate = k[A] [B] D) Rate = k[A]
B) Rate = k[A]2 [B] E) Rate = k[A]3
C) Rate = k[A] [B]2
Chapter 16: Kinetics: Rates and Mechanisms of Chemical Reactions
Page 269
7. For the reaction
2A + B + 2C → D + E
the following initial rate data were collected at constant temperature. Determine the correct rate
law for this reaction. All units are arbitrary.
Trial [A] [B] [C] Rate
1 0.225 0.150 0.350 0.0217
2 0.320 0.150 0.350 0.0439
3 0.225 0.250 0.350 0.0362
4 0.225 0.150 0.600 0.01270
A) Rate = k[A][B][C] D) Rate = k [A][B]2[C] –1
B) Rate = k [A]2[B][C] E) none of the above
C) Rate = k [A]2[B][C]–1
8. The rate constant for a reaction is 4.65 L mol–1s–1. What is the overall order of the
reaction?
A) zero
B) first
C) second
D) third
E) More information is needed to determine the overall order.
9. Sulfuryl chloride, SO2Cl2(g), decomposes at high temperature to form SO2(g) and Cl2(g).
The rate constant at a certain temperature is 4.68 × 10–5s–1. What is the order of the reaction?
A) zero
B) first
C) second
D) third
E) More information is needed to determine the order.
10. When the reaction A → B + C is studied, a plot of ln[A]t vs. time gives a straight
line with a negative slope. What is the order of the reaction?
A) zero
B) first
C) second
D) third
E) More information is needed to determine the order.
Chapter 16: Kinetics: Rates and Mechanisms of Chemical Reactions
11. When the reaction A → B + C is studied, a plot 1/[A]t vs. time gives a straight line
with a positive slope. What is the order of the reaction?
A) zero
B) first
C) second
D) third
12. Which of the following sets of units could be appropriate for a zero-order rate constant?
A) s–1 B) L mol–1 s–1 C) L2 mol–2 s–1 D) L3 mol–3 s–1 E) mol L–1 s–1
13. Which one of the following sets of units is appropriate for a second-order rate constant?
A) s–1 B) mol L–1 s–1 C) L mol–1 s–1 D) mol2 L–2 s–1 E) L2 mol–2 s–1
14. Which one of the following sets of units is appropriate for a third-order rate constant?
A) s–1 B) mol L–1 s–1 C) L mol–1 s–1 D) L2 mol–2 s–1 E) L3 mol–3 s–1
15. A reaction has the following rate law:
Rate = k[A][B]2
In experiment 1, the concentrations of A and B are both 0.10 mol L–1; in experiment 2, the
concentrations are both 0.30 mol L–1. If the temperature stays constant, what is the value of the
ratio, Rate(2)/Rate(1)?
A) 3.0 B) 6.0 C) 9.0 D) 18 E) 27
16. Ammonium cyanate (NH4CNO) reacts to form urea (NH2CONH2). At 65°C the rate
constant, k, is 3.60 L mol–1s–1. What is the rate law for this reaction?
A) Rate = 3.60 L mol–1s–1[NH4CNO]
B) Rate = 3.60 L mol–1s–1[NH4CNO]2
C) Rate = 0.28 mol L–1 s–1[NH4CNO]
D) Rate = 0.28 mol L–1 s–1[NH4CNO]2
E) Rate = 3.60 L mol–1s–1[NH2CONH2]–1
Chapter 16: Kinetics: Rates and Mechanisms of Chemical Reactions
17. 2NOBr(g) → 2NO(g) + Br2(g)
[NOBr](mol L–1) Rate (mol L–1s–1)
0.0450 1.62 × 10–3
0.0310 7.69 × 10–4
0.0095 7.22 × 10–5
Based on the initial rate data above, what is the value of the rate constant?
A) 0.0360 L mol–1s–1 D) 27.8 L mol–1s–1
B) 0.800 L mol–1s–1 E) 0.0360 s–1
C) 1.25 L mol–1s–1
18. A study of the decomposition reaction 3RS2 → 3R + 6S yields the following initial
rate data
[RS2](mol L–1) Rate (mol/(L·s))
0.150 0.0394
0.250 0.109
0.350 0.214
0.500 0.438
What is the rate constant for the reaction?
A) 0.0103 L mol–1s–1 D) 1.17 L mol–1s–1
B) 0.263 L mol–1s–1 E) 1.75 L mol–1s–1
C) 0.571 L mol–1s–1
19. Sulfur trioxide can undergo decomposition according to the equation
2SO3 → 2SO2 + O2
For this reaction, rate = -0 0.5[SO3]/t = k[SO3]2. If the reaction rate is 1.75 × 10-7 mol L-1
min-1 when the concentration of sulfur trioxide is 5.4 × 10-3 mol L-1, what is the value of the rate
constant k?
A) 3.2 × 10-5 L mol-1 min-1 D) 3.0 × 10-3 L mol-1 min-1
B) 1.6 × 10-5 L mol-1 min-1 E) 1.6 × 10-2 L mol-1 min-1
C) 6.0 × 10-3 L mol-1 min-1
20. Sucrose decomposes to fructose and glucose in acid solution. When ln [sucrose] is
plotted vs. time, a straight line with slope of –0.208 hr–1 results. What is the rate law for the
reaction?
A) Rate = 0.208 hr–1 [sucrose]2 D) Rate = 0.0433 hr [sucrose]
B) Rate = 0.208 hr–1 [sucrose] E) Rate = 0.208 mol L–1hr–1 [sucrose]0
C) Rate = 0.0433 hr [sucrose]2
Chapter 16: Kinetics: Rates and Mechanisms of Chemical Reactions
21. Tetrafluoroethylene, C2F4, can be converted to octafluorocyclobutane which can be used
as a refrigerant or an aerosol propellant. A plot of 1/[C2F4] vs. time gives a straight line with a
slope of 0.0448 L mol–1s–1. What is the rate law for this reaction?
A) Rate = 0.0448 (L mol–1s–1)[C2F4] D) Rate = 22.3 (mol L–1s)[C2F4]2
B) Rate = 22.3 (mol L–1s)[C2F4] E) Rate = 0.0448 s–1 [C2F4]
C) Rate = 0.0448 (L mol–1s–1)[C2F4]2
22. A reaction is first-order with respect to the reactant R. Which of the following plots will
produce a straight line?
A) [R] vs. 1/time D) 1/[R]2 vs. time
B) 1/[R] vs. time E) ln[R] vs. time
C) [R]2 vs. time
23. A reaction is second-order with respect to the reactant R. Which of the following plots
will produce a straight line?
A) [R] vs. 1/time D) 1/[R]2 vs. time
B) 1/[R] vs. time E) ln[R] vs. time
C) [R]2 vs. time
24. The reaction X → Y is first-order overall and first-order with respect to the reactant X.
The result of doubling the initial concentration of X will be to
A) shorten the half-life of the reaction.
B) increase the rate constant of the reaction.
C) decrease the rate constant of the reaction.
D) shorten the time taken to reach equilibrium.
E) double the initial rate.
25. The decomposition of hydrogen peroxide is a first-order process with a rate constant of
1.06 × 10–3 min–1. How long will it take for the concentration of H2O2 to drop from 0.0200 M to
0.0120 M?
A) < 1 min B) 7.55 min C) 481 min D) 4550 min E) 31,400 min
Chapter 16: Kinetics: Rates and Mechanisms of Chemical Reactions
26. Cyclopropane is converted to propene in a first-order process. The rate constant is 5.4 ×
10–2 hr–1. If the initial concentration of cyclopropane is 0.150 M, what will its concentration be
after 22.0 hours?
A) 0.0457 M
B) 0.105 M
C) 0.127 M
D) 0.492 M
E) none of the above
27. A gas-phase decomposition is first-order with respect to the reactant, R. If the initial
concentration of R is 1.0 × 10-4 mol L-1 and the rate constant k = 1.08 × 10-6 s-1, what
concentration of R remains after 25 days?
A) 1.0 × 10–3 mol L-1 D) 4.3 × 10-5 mol L-1
B) 1.0 × 10-4 mol L-1 E) 9.7 × 10-6 mol L-1
C) 9.6 × 10-5 mol L-1
28. The rate law for the reaction 3A → 2B is rate = k[A] with a rate constant of 0.0447 hr–1.
What is the half-life of the reaction?
A) 0.0224 hr B) 0.0645 hr C) 15.5 hr D) 22.4 hr E) 44.7 hr
29. The rate law for the rearrangement of CH3NC to CH3CN at 800 K is Rate = (1300 s–
1)[CH3NC]. What is the half-life for this reaction?
A) 7.69 × 10–4 s B) 5.3 × 10–4 s C) 1.9 × 10–3 s D) 520 s E) 1920 s
30. The rate constant for the reaction 3A → 4B is 6.00 × 10–3 L mol–1min–1. How long will it
take the concentration of A to drop from 0.75 M to 0.25 M?
A) 2.2 × 10–3 min D) 440 min
B) 5.5 × 10–3 min E) 5.0 × 102 min
C) 180 min
31. The active ingredient in an over the counter pain killer analgesic decomposes with a rate
constant, k = 9.05 × 10-4 day-1. How many days does it take for 15% of the original ingredient to
decompose?
A) 730 days B) 414 days C) 365 days D) 180 days E) 78 days
Chapter 16: Kinetics: Rates and Mechanisms of Chemical Reactions
32. Butadiene, C4H6 (used to make synthetic rubber and latex paints) reacts to C8H12 with a
rate law of rate = 0.014 L/(mol·s) [C4H6]2. What will be the concentration of C4H6 after 3.0
hours if the initial concentration is 0.025 M?
A) 0.0052 M B) 0.024 M C) 43 M D) 190 M E) 0.0000 M
33. The rate law for the reaction 3A → C is
Rate = 4.36 × 10–2 L mol–1 hr–1[A]2
What is the half-life for the reaction if the initial concentration of A is 0.250 M?
A) 0.0109 hr B) 0.0629 hr C) 15.9 hr D) 23.9 hr E) 91.7 hr
34. The decomposition of SOCl2 is first-order in SOCl2. If the half-life for the reaction is 4.1
hr, how long would it take for the concentration of SOCl2 to drop from 0.36 M to 0.045 M?
A) 0.52 hr B) 1.4 hr C) 12 hr D) 33 hr E) > 40 hr
35. The reaction CH3NC(g) → CH3CN(g) is first-order with respect to methyl isocyanide,
CH3NC. If it takes 10.3 minutes for exactly one quarter of the initial amount of methyl
isocyanide to react, what is the rate constant in units of min–1?
A) –0.135 min–1 D) 0.135 min–1
B) 0.0279 min–1 E) 35.8 min–1
C) 0.089 min–1
36. A reactant R is being consumed in a first-order reaction. What fraction of the initial R is
consumed in 4.0 half-lives?
A) 0.94 B) 0.87 C) 0.75 D) 0.13 E) 0.063
37. A first-order reaction has a half-life of 20.0 minutes. Starting with 1.00 × 1020 molecules
of reactant at time t = 0, how many molecules remain unreacted after 100.0 minutes?
A) 1.00 × 104 molecules D) 5.00 × 1020 molecules
B) 2.00 × 1019 molecules E) none of the above
C) 3.20 × 1016 molecules
38. Carbon-14 is a radioactive isotope which decays with a half-life of 5730 years. What is
the first-order rate constant for its decay, in units of years–1?
A) 5.25 × 10–5 years–1 D) 3.49 × 10–4 years–1
B) 1.21 × 10–4 years–1 E) 3.97 × 103 years–1
C) 1.75 × 10–4 years–1
Chapter 16: Kinetics: Rates and Mechanisms of Chemical Reactions
39. The radioactive isotope tritium decays with a first-order rate constant k of 0.056 year–1.
What fraction of the tritium initially in a sample is still present 30 years later?
A) 0.19 B) 0.60 C) 0.15 D) 2.8 × 10–38 E) none of the above
40. Dinitrogen tetraoxide, N2O4, decomposes to nitrogen dioxide, NO2, in a first-order
process. If k = 2.5 × 103 s–1 at –5°C and k = 3.5 × 104 s–1 at 25°C, what is the activation energy
for the decomposition?
A) 0.73 kJ/mol D) 580 kJ/mol
B) 58 kJ/mol E) > 1000 kJ/mol
C) 140 kJ/mol
41. Ammonia will react with oxygen in the presence of a copper catalyst to form nitrogen
and water. From 164.5°C to 179.0°C, the rate constant increases by a factor of 4.27. What is the
activation energy of this oxidation reaction?
A) 24.5 kJ/mol D) 1630 kJ/mol
B) 165 kJ/mol E) > 104 kJ/mol
C) 242 kJ/mol
42. In going from room temperature (25.0 °C) to 10 °C above room temperature, the rate of
a reaction doubles. Calculate the activation energy for the reaction.
A) 157.2 kJ/mol D) 6.4 kJ/mol
B) 103.8 kJ/mol E) <1 kJ/mol
C) 52.9 kJ/mol
43. A boiled egg can be cooked at 100.0 °C in exactly 5 minutes. At an altitude of around
2000 m where the boiling point of water is 93.0 °C, it takes exactly 7.5 minutes to cook the egg
to the same amount. What is the activation energy for the reaction involved when an egg is
boiled?
A) 0.5 kJ/mol
B) 4.5 kJ/mol
C) 7.9 kJ/mol
D) 66 kJ/mol
E) >100 kJ/mol
Chapter 16: Kinetics: Rates and Mechanisms of Chemical Reactions
44. If the activation energy of a reaction decreases by 10.0 kJ/mol, from 100.0 to 90.0
kJ/mol, what effect will this have on the rate of reaction at 298K?
A) The rate will increase, by a factor of more than 50.
B) The rate will decrease, by a factor of more than 50.
C) The rate will increase, by a factor of less than 50.
D) The rate will decrease, by a factor of less than 50.
E) The rate will not change unless temperature changes.
45. A rate constant obeys the Arrhenius equation, the factor A being 2.2 × 1013 s–1 and the
activation energy being 150. kJ mol–1. What is the value of the rate constant at 227°C, in s–1?
A) 2.1 × 1013 s–1 D) 4.7 × 10–3 s–1
B) 6.7 × 10–22 s–1 E) none of the above
C) 1.5 × 1011 s–1
46. A reaction has an activation energy of 195.0 kJ/mol. When the temperature is increased
from 200.°C to 220.°C, the rate constant will increase by a factor of
A) 1.1. B) 4.3 × 104. C) 3.2. D) 7.5. E) none of the above.
47. The decomposition of dinitrogen pentaoxide to nitrogen dioxide and oxygen follows
first-order kinetics and has an activation energy of 102 kJ/mol. By what factor will the fraction
of collisions with energy greater than or equal to the activation energy increase if the reaction
temperature goes from 30°C to 60°C?
A) 1.00 B) 1.10 C) 2.00 D) 4.00 E) 38.4
48. The decomposition of dinitrogen pentaoxide has an activation energy of 102 kJ/mol and
H°rxn = + 55 kJ/mol. What is the activation energy for the reverse reaction?
A) 27 kJ/mol
B) 47 kJ/mol
C) 55 kJ/mol
D) 102 kJ/mol
E) More information is needed, since this is a Hess’s law calculation.
Chapter 16: Kinetics: Rates and Mechanisms of Chemical Reactions
49. The kinetics of the decomposition of dinitrogen pentaoxide is studied at 50°C and at
75°C. Which of the following statements concerning the studies is correct?
A) The rate at 75°C will be greater than the rate at 50°C because the activation energy
will be lower at 75°C than at 50°C.
B) The rate at 75°C will be greater than the rate at 50°C because the activation energy
will be higher at 75°C than at 50°C.
C) The rate at 75°C will be less than the rate at 50°C because the molecules at higher
speeds do not interact as well as those at lower speeds.
D) The rate at 75°C will be greater than at 50°C because the concentration of a gas
increases with increasing temperature.
E) The rate at 75°C will be greater than the rate at 50°C because the number of
molecules with enough energy to react increases with increasing temperature.
50. An increase in temperature increases the reaction rate because
A) a greater fraction of the collisions have the correct orientation of molecules.
B) the activation energy of the reaction will increase.
C) the activation energy of the reaction will decrease.
D) temperature acts as a catalyst in chemical reactions.
E) more collisions will have enough energy to exceed the activation energy.
51. In an exothermic reaction,
A) the forward reaction is slower than the reverse reaction.
B) the reaction rate will speed up with time.
C) the collision energy of the reactants will be greater than that of the products.
D) the forward reaction will have a lower activation energy than the reverse reaction.
E) the activation energy will change as the reaction progresses.
52. Reaction intermediates differ from activated complexes in that
A) they are stable molecules with normal bonds and are frequently isolated.
B) they are molecules with normal bonds rather than partial bonds and can
occasionally be isolated.
C) they are intermediate structures which have characteristics of both reactants and
products.
D) they are unstable and can never be isolated.
E) all reactions involve reaction intermediates, but not all have activated complexes.