Test Bank General Chemistry, 10th edition 21
57. Dinitrogen tetroxide decomposes to form nitrogen dioxide in a second-order reaction:
N2O4(g) → 2NO2(g)
At 400.0 K, the rate constant for this reaction has been measured to be 2.9 108 L/(mol · s).
Suppose 0.222 mol of N2O4(g) is placed in a sealed 41.7-L container at 400.0 K and allowed
to react. What is the total pressure inside the vessel after 32.9 ns has elapsed? (R = 0.0821
(L · atm)/(K · mol))
A)
0.183 atm
B)
0.175 atm
C)
0.166 atm
D)
0.524 atm
E)
0.350 atm
58. At 500oC, cyclopropane (C3H6) reacts to form its isomer, propene (C3H6). The reaction is
first-order, and the rate constant is 6.7 10–4 s–1. If the initial concentration of cyclopropane
is 0.500 M and the initial concentration of propene is 0, determine the time required for the
concentration of propene to reach 0.100 M.
A)
3.4 103 s
B)
3.3 102 s
C)
1.2 104 s
D)
7.5 102 s
E)
2.4 103 s
59. A second-order reaction starts with an initial concentration of 0.100 mol/L of the reactant. If
the rate constant is 3.6 10–2 L/(mol · s), what is the time required to decrease the initial
concentration to 0.050 mol/L?
A)
280 s
B)
420 s
C)
19.3 s
D)
1.39 s
E)
830 s
Test Bank General Chemistry, 10th edition 22
60. The half-life of a reaction is
A)
twice as long for a second-order reaction as it is for a first-order reaction.
B)
one-half of the time the reaction will take to go to completion.
C)
how long the reaction can run before stopping.
D)
the time it takes for the amount of product formed to equal half the initial amount
of reactant.
E)
the time it takes for the reactant concentration to decrease to one-half of its initial
value.
61. The reaction A → products is first-order in A. If the concentration of A is cut in half, the
half-life of the reaction will
A)
decrease by a factor of 1/2.
B)
double.
C)
decrease by a factor of 1/4.
D)
remain constant.
E)
quadruple.
62. The reaction 3NO → N2O + NO2 is found to obey the rate law Rate = k[NO]2. If the first
half-life of the reaction is found to be 2.0 s, what is the length of the fourth half-life?
A)
4.0 s
B)
8.0 s
C)
2.0 s
D)
16.0 s
E)
12.0 s
63. For which order reaction is the half-life of the reaction proportional to 1/k (k is the rate
constant)?
A)
second-order reaction only
B)
first-order reaction only
C)
zero-order reaction only
D)
all of the above
E)
none of the above
64. Which of the following corresponds to the correct equation for the half-life of a first-order
reaction?
A)
B)
C)
D)
E)
65. A first-order chemical reaction is observed to have a rate constant of 25 min–1. What is the
corresponding half-life for the reaction?
A)
1.7 s
B)
1.7 min
C)
36 min
D)
2.4 s
E)
35.8 s
66. In a first-order reaction, the half-life is 137 minutes. What is the rate constant?
A)
1.22 10–4 s–1
B)
5790 s–1
C)
0.304 s–1
D)
5.06 10–3 s–1
E)
8.43 10–5 s–1
67. The OH· radical disproportionates according to the elementary chemical reaction
This reaction is second-order in OH·. The rate constant for the reaction is 2.0 10–12
cm3/molecules at room temperature. If the initial OH· concentration is 1.7 1013
molecules/cm3, what is the first half-life for the reaction?
A)
3.4 101 s
B)
2.9 10–2 s
C)
1.5 10–2 s
D)
3.5 1011 s
E)
5.9 10–14 s
68. For a certain reaction of the general form aA → products, a plot of the experimental data as
[A] versus time is linear. What is the reaction order with respect to reactant A?
A)
zero
B)
first
C)
second
D)
fourth
E)
third
69. For a certain reaction of the general form aA → products, the experimental data plotted as
1/[A] versus time is linear. The slope of this plot must equal
A)
–1.
B)
the rate constant.
C)
one over the rate constant.
D)
the negative of the rate constant.
E)
1.
70. For the hypothetical reaction A → products, the concentration of A was monitored over
time. From the following graph, what is the rate constant for the decomposition of A?
A)
–0.02735 s–1
B)
2.3026 s–1
C)
–2.3026 s–1
D)
0.02735 s–1
E)
0.01188 s–1
71. For the hypothetical reaction aA → products, the experimental data showed the following
behavior (below). What is the reaction order with respect to reactant A?
A)
first-order
B)
second-order
C)
zero-order
D)
third-order
E)
fourth-order
72. For the hypothetical reaction A → products, the concentration of A was monitored with
time. From the following graph, what is the rate constant for the decomposition of A?
A)
–0.07238 M–1 s–1
B)
–10.00 M–1 s–1
C)
0.07238 M–1 s–1
D)
10.00 M–1 s–1
E)
0.007238 M–1 s–1
73. For the hypothetical reaction aA → products, the concentration of A was monitored with
time. Given the following graph of the experimental data, what is the rate constant for the
loss of reactant A?
A)
2.42
−min−
B)
400.00
−min−
C)
-2.42
−min−
D)
-400
−min−
E)
24.2
−min−
74. Which of the following statements best describes the condition(s) needed for a successful
formation for a product according to the collision model?
A)
The relative orientation of the particles has an effect only if the kinetic energy of
the particles is below some minimum value.
B)
The collision must involve a sufficient amount of energy, provided from the
motion of the particles, to overcome the activation energy.
C)
The relative orientation of the particles must allow for formation of the new bonds
in the product.
D)
The energy of the incoming particles must be above a certain minimum value, and
the relative orientation of the particles must allow for formation of new bonds in
the product.
E)
The relative orientation of the particles has little or no effect on the formation of
the product.
75. Which of the following changes will affect the rate constant of a reaction?
1.
Increasing or decreasing the reaction temperature.
2.
Adding a catalyst.
3.
Increasing or decreasing the reactant concentrations.
A)
1 only
B)
2 only
C)
3 only
D)
1 and 2
E)
1, 2, and 3
76. Which of the following changes will affect the activation energy of a reaction?
1.
Increasing or decreasing the reaction temperature.
2.
Adding a catalyst.
3.
Increasing or decreasing the reactant concentrations.
A)
1 only
B)
2 only
C)
3 only
D)
1 and 2
E)
2 and 3
77. What would happen if the kinetic energy of the reactants were not enough to provide the
needed activation energy?
A)
The rate of the reaction would tend to increase.
B)
The reactants would continue to exist in their present form.
C)
The activated complex would be converted into products.
D)
The products would be produced at a lower energy state.
E)
The products would form at an unstable energy state.
78. The main reason for the increase in reaction rate with temperature is that
A)
the fraction of high-energy molecules increases exponentially with temperature.
B)
the activation energy increases rapidly with temperature.
C)
a 10°C temperature rise results in the rate doubling.
D)
there is a dramatic increase in the number of collisions.
E)
heat acts as a catalyst.
79. When the concentrations of the reactants are increased, the rate of the reaction increases.
This is best explained by
A)
an increase in the fraction of molecules that have enough energy to react.
B)
an increase in the rate constant.
C)
an increase in the average potential energy of the molecules.
D)
an increase in the frequency of the molecular collisions.
E)
an increase in the kinetic energy of the molecules.
80. The rates of most chemical reactions are sensitive to a change in the temperature of the
reaction system. The increase in rate as the temperature increases is best explained by
A)
an increase in the collision frequency.
B)
an increase in the number of high-energy molecules.
C)
a decrease in the collision frequency.
D)
an increase in the activation energy.
E)
a decrease in the activation energy.
81. The potential-energy diagram below describes the hypothetical reaction A + B → C + D.
Assuming the y-axis label refers to the enthalpy(H) per mol, which of the following
statements concerning this reaction coordinate is/are correct?
1.
The forward reaction is exothermic.
2.
The forward reaction rate is proportional to the change in enthalpy (H) of the
forward reaction.
3.
Ea(forward) − Ea(reverse) is equal to the change in enthalpy (H) of the
forward reaction.
A)
1 only
B)
2 only
C)
3 only
D)
1 and 3
E)
1, 2, and 3
82. Which of the following is not a postulate of collision theory?
A)
Reactant molecules must collide to react.
B)
Reactant molecules must collide with a certain minimum energy in order to form
products.
C)
Reactant molecules must collide with the correct orientation in order to form
products.
D)
The rate constant is directly proportional to the energy of activation.
E)
The maximum in the potential energy curve, the activation energy, is determined
by the structure of the activated complex or transition state.
83. For the formation of 1 mol of nitrosyl chloride at a given temperature, H = –44 kJ.
NO(g) + ½ Cl2(g) → NOCl(g)
The activation energy for this reaction is 59 kJ/mol. What is the activation energy for the
reverse reaction?
A)
59 kJ/mol
B)
15 kJ/mol
C)
103 kJ/mol
D)
–44 kJ/mol
E)
–103 kJ/mol
84. For the following reaction producing 1 mol of oxygen gas at a particular temperature,
H = –200 kJ.
NO(g) + O3(g) → NO2(g) + O2(g)
The activation energy is 11 kJ/mol. What is the activation energy for the reverse reaction?
A)
11 kJ/mol
B)
200 kJ/mol
C)
222 kJ/mol
D)
188 kJ/mol
E)
211 kJ/mol
85. For the first-order reaction
½ N2O4(g) → NO2(g); H = 28.6 kJ
the activation energy is 53.7 kJ/mol. What is the activation energy for the reverse reaction?
A)
15.2 kJ/mol
B)
82.3 kJ/mol
C)
–53.7 kJ/mol
D)
25.1 kJ/mol
E)
53.7 kJ/mol
86. The rate constant for a first-order reaction is 1.6 10–2 s–1 at 668 K and 5.1 10–2 s–1 at
916 K. What is the activation energy? (R = 8.31 J/(mol · K))
A)
11 kJ/mol
B)
14 kJ/mol
C)
23 kJ/mol
D)
2900 kJ/mol
E)
24 kJ/mol
87. The rate constants for the first-order decomposition of a compound are 6.19 10–4 s–1 at
43°C and 2.71 10–3 s–1 at 65°C. What is the value of the activation energy for this
reaction? (R = 8.31 J/(mol · K))
A)
0.677 kJ/mol
B)
25.9 kJ/mol
C)
0.558 kJ/mol
D)
59.6 kJ/mol
E)
1.56 kJ/mol
88. For the first-order reaction
½ N2O4(g) → NO2(g); H = 28.6 kJ
the rate constant is k = 9.29 104 s–1 at –20°C, and the activation energy is 53.7 kJ/mol.
What is the rate constant at 21°C?
A)
1.08 105 s–1
B)
9.29 104 s–1
C)
1.74 105 s–1
D)
3.27 106 s–1
E)
4.94 104 s–1