Chapter 13 – Chemical Kinetics
37. A city’s water supply is contaminated with a toxin at a concentration of 0.63 mg/L. For the
water to be safe for drinking, the concentration of this toxin must be below 1.5 x 10-3 mg/L.
Fortunately, this toxin decomposes to a safe mixture of products by first-order kinetics with a
rate constant of 0.27 day–1. How long will it take for the water to be safe to drink?
38. A reaction was experimentally determined to follow the rate law, Rate = k[A] where k =
0.15 s-1. Starting with [A]o = 0.225M, how many seconds will it take for [A]t = 0.0350M?
Chapter 13 – Chemical Kinetics
39. A reaction was experimentally determined to follow the rate law, Rate = k[A]2 where k =
0.456 s-1M-1. Starting with [A]o = 0.500 M, how many seconds will it take for [A]t = 0.250
M?
40. Benzoyl chloride, C6H5COCl, reacts with water to form benzoic acid, C6H5COOH, and
hydrochloric acid. This first-order reaction is 25% complete after 26 s. How much longer
would one have to wait in order to obtain 99% conversion of benzoyl chloride to benzoic
acid?
Chapter 13 – Chemical Kinetics
41.
A certain reaction A → products is second order with respect to A with a rate constant, k, 0.122 M-1min-1. Starting with [A]o
= 1.01M, how many seconds will it take for A to reach a concentration of 0.750M?
42.
A certain reaction A → products is second order with respect to A. If it takes 45 min to reduce the concentration of A from
0.350 M to 0.125 M, what is the rate constant for this reaction?
Chapter 13 – Chemical Kinetics
43. A reaction is experimentally found to follow the rate law, Rate = k[A]2 where k = 0.355
M-1min-1. Starting with [A]o = 1.55 M, how many seconds will it take for [A]t = 0.150M?
44. A reaction is experimentally found to follow the rate law, Rate = k[A]2 where k = 0.130
M-1min-1. Starting with [A]o = 2.50 M, how many seconds will it take for [A]t = 1.25 M?
Chapter 13 – Chemical Kinetics
45.
At 25C, the second-order reaction NOCl(g) → NO(g) + 1/2Cl2(g)is 50% complete after 5.82 hours when the initial
concentration of NOCl is 4.46 mol/L. How long will it take for the reaction to be 75% complete?
Chapter 13 – Chemical Kinetics
46.
For the reaction X + Y → Z, the reaction rate is found to depend only upon the concentration of X. A plot of 1/X verses time
gives a straight line.
What is the rate law for this reaction?
Chapter 13 – Chemical Kinetics
47.
The reaction 2NO2(g) → 2NO(g) + O2(g) is suspected to be second order in NO2. Which of the following kinetic plots would
be the most useful to confirm whether or not the reaction is second order?
48.
The thermal decomposition of acetaldehyde, CH3CHO → CH4 + CO, is a second-order reaction. The following data were
obtained at 518C.
Chapter 13 – Chemical Kinetics
49.
The thermal decomposition of acetaldehyde, CH3CHO → CH4 + CO, is a second-order reaction. The following data were
obtained at 518C.
Based on the data given, what is the half-life for the disappearance of acetaldehyde?
50.
For the chemical reaction A → B + C, a plot of [A]t versus time is found to give a straight line with a negative slope. What is
the order of reaction with respect to A?
Chapter 13 – Chemical Kinetics
51.
For the chemical reaction A → C, a plot of 1/[A]t versus time was found to give a straight line with a positive slope. What is
the order of reaction?
52.
The graphs below all refer to the same reaction. What is the order of this reaction?
Chapter 13 – Chemical Kinetics
53. For what order reaction does the half-life get longer as the initial concentration increases?
54. For a second order reaction, the half-life is equal to
Chapter 13 – Chemical Kinetics
55.
Concerning the decomposition of A, A → products, which of the following methods could be used to determine the order of
the reaction with respect to A?
I. Plot [A] vs time, ln[A] vs time, and 1/[A] vs time and identify which plot yields a straight line.
II. Vary the concentration of A and note by what factor the rate changes.
III. Identify if successive half lives of A double, halve, or stay constant.
56. In general, to calculate the rate constant for a second order reaction with respect to A,
given an initial and final concentration as well as the time required for this change, which
equation should be used?
Chapter 13 – Chemical Kinetics
57.
In general, to calculate the rate constant for a first order decomposition reaction,
A → products, given the time needed to decrease the initial concentration by one half, which equation should be used?
58. In general, to calculate the time required for a given initial concentration to decrease by
35% given the rate constant with units of 1/M-1s-1, which equation should be used?
Chapter 13 – Chemical Kinetics
59. In general, to calculate the activation energy for an elementary step given the rate
constants at two different temperatures, which equation should be used?
60.
Which one of the following changes would alter the rate constant (k) for the reaction 2A + B → products?
Chapter 13 – Chemical Kinetics
61. The Arrhenius equation is k = Ae–Ea/RT. The slope of a plot of ln k vs. 1/T is equal to
62.
What is the slope of an Arrhenius plot for the following reaction?
2NOCl → 2NO + Cl2
Chapter 13 – Chemical Kinetics
63.
The activation energy for the reaction CH3CO → CH3 + CO is 71 kJ/mol. How many times greater is the rate constant for
this reaction at 170C than at 150C?
64. If Ea for a certain biological reaction is 50. kJ/mol, by what factor (how many times) will
the rate of this reaction increase when body temperature increases from 37C (normal) to
40C (fever)?
Chapter 13 – Chemical Kinetics
65. At 25C, by what factor is the reaction rate increased by a catalyst that reduces the
activation energy of the reaction by 1.00 kJ/mol?
66. At 30C, by how much is a reaction’s activation energy decreased by the addition of a
catalyst if the catalyst triples the reaction rate?
Chapter 13 – Chemical Kinetics
67.
The activation energy for the following reaction is 60. kJ/mol.
Sn2+ + 2Co3+ → Sn4+ + 2Co2+
By what factor (how many times) will the rate constant increase when the temperature is raised from 10C to 28C?
68. The isomerization of cyclopropane follows first order kinetics. The rate constant at 700 K
is 6.20 10–4 min–1, and the half-life at 760 K is 29.0 min. Calculate the activation energy for
Chapter 13 – Chemical Kinetics
69.
The isomerization of methyl isocyanide, CH3NC → CH3CN, follows first-order kinetics. The half-lives were found to be 161
min at 199C and 12.5 min at 230C. Calculate the activation energy for this reaction.
Chapter 13 – Chemical Kinetics
70.
Calculate the activation energy, in kJ/mol, for the redox reaction
Sn2+ + 2Co3+ → Sn4+ + 2Co2+.
71.
The reaction C4H10 → C2H6 + C2H4 has an activation energy (Ea) of 350 kJ/mol, and the Ea of the reverse reaction is 260
kJ/mol. Estimate H, in kJ/mol, for the reaction as written above.
Chapter 13 – Chemical Kinetics
72.
The activation energy for the following first-order reaction is 102 kJ/mol.
N2O5(g) → 2NO2(g) + 1/2O2(g)
The value of the rate constant (k) is 1.35 10–4 s–1 at 35C. What is the value of k at 0C?
73. Given that Ea for a certain biological reaction is 48 kJ/mol and that the rate constant is 2.5
10–2 s–1 at 15C, what is the rate constant at 37C?