and the mechanism MSC: Conceptual
Under certain conditions the reaction H2O2 + 3I– + 2H+ → I3– + 2H2O occurs by the
following series of steps:
k1
Step 1.
H2O2 + H+ H3O2+
k–1
111. Which of the steps would be called the rate-determining step?
A)
1
B)
2
C)
3
D)
4
E)
5
112. The rate constant k for the reaction would be given by
A)
k = k2
B)
k = k2k3
C)
k = k2K
D)
k = k5
E)
k = Kk2k3k4k5
113. The rate law for the reaction would be:
A)
[I3]/t = k[H2O2]
B)
[I3]/t = k[H2O2][H+][I–]
C)
[I3]/t = k[H2O2][H+]
D)
[I3]/t = k[H2O2][I–]
E)
[I3]/t = k[H2O2][H+]2[I–]–3
114. The reaction:
2A + B → C
has the following proposed mechanism:
Step 1: A + B D (fast equilibrium)
Step 2: D + B → E
Step 3: E + A → C + B
If step 2 is the rate-determining step, then the rate of formation of C should equal:
A)
k[A]
B)
k[A]2[B]
C)
k[A]2[B]2
D)
k[A][B]
E)
k[A][B]2
115. The reaction 2NO + O2 → 2NO2 obeys the rate law – = kobsd[NO]2[O2].
Which of the following mechanisms is consistent with the experimental rate law?
A)
NO + NO → N2O2 (slow)
N2O2 + O2 → 2NO2 (fast)
B)
NO + O2NO3 (fast equilibrium)
NO3 + NO → 2NO2 (slow)
C)
2NO N2O2 (fast equilibrium)
N2O2 → NO2 + O (slow)
NO + O → NO2 (fast)
D)
O2 + O2 → O2 + O2 (slow)
O2 + NO → NO2 + O (fast)
O + NO → NO2 (fast)
E)
none of these
116. The rate constant k is dependent on
I.
the concentration of the reactant
II.
the nature of the reactants
III.
the temperature
IV.
the order of the reaction
A)
none of these
B)
one of these
C)
two of these
D)
three of these
E)
all of these
The questions below refer to the following diagram:
117. Why is this reaction considered to be exothermic?
A)
Because energy difference B is greater than energy difference C.
B)
Because energy difference B is greater than energy difference A.
C)
Because energy difference A is greater than energy difference C.
D)
Because energy difference B is greater than energy difference C plus energy
difference A.
E)
Because energy difference A and energy difference C are about equal.
118. At what point on the graph is the activated complex present?
A)
point W
B)
point X
C)
point Y
D)
point Z
E)
none of these
119. If the reaction were reversible, would the forward or the reverse reaction have a higher
activation energy?
A)
The diagram shows no indication of any activation energy.
B)
The forward and reverse activation energies are equal.
C)
The forward activation energy would be greater.
D)
The reverse activation energy would be greater.
E)
None of these.
Potential Energy
Reaction Process
W
X
Y
Z
A
B
C
120. What would happen if the kinetic energy of the reactants was not enough to provide the
needed activation energy?
A)
The products would be produced at a lower energy state.
B)
The rate of the reaction would tend to increase.
C)
The activated complex would convert into products.
D)
The reactants would continue to exist in their present form.
E)
The products would form at an unstable energy state.
121. The rate constant for a reaction at 40.0°C is exactly 3 times that at 20.0°C. Calculate the
Arrhenius energy of activation for the reaction.
A)
9.13 kJ/mol
B)
5.04 kJ/mol
C)
41.9 kJ/mol
D)
3.00 kJ/mol
E)
none of these
Use the potential energy diagram shown to answer the following:
122. Which letter shows the activation energy (without use of a catalyst)?
A)
a
B)
b
C)
c
D)
d
E)
e
123. Which letter shows the change in energy for the overall reaction?
a
b
cd
e
A)
a
B)
b
C)
c
D)
d
E)
e
124. Which letter shows the activation energy using a catalyst?
A)
a
B)
b
C)
c
D)
d
E)
e
The questions below refer to the following information: The rate constant k for the reaction
shown below is 2.6 10–8 L/mol s when the reaction proceeds at 300.0 K. The activation
energy is 98000 J/mol. (The universal gas constant, R, is 8.314 J/mol·K)
2NOCl → 2NO + Cl2
125. Determine the magnitude of the frequency factor for the reaction.
A)
1.2 108
B)
4.6 109
C)
3.0 109
D)
2.7 108
E)
9.1 109
126. If the temperature changed to 310 K, the rate constant k would change. The ratio of k at 310
K to k at 300.0 K is closest to what whole number?
A)
1
B)
2
C)
3
D)
4
E)
5
127. Use the following information to determine the activation energy for the reaction shown
here:
Temperature
(K)
Rate Constant
(L/mol·s)
1400
0.143
1500
0.685
A)
J/mol
B)
J/mol
C)
J/mol
D)
J/mol
E)
J/mol
128. When ethyl chloride, CH3CH2Cl, is dissolved in 1.0 M NaOH, it is converted into ethanol,
CH3CH2OH, by the reaction:
At 25°C the reaction is first order in CH3CH2Cl, and the rate constant is 3.1 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 40.°C?
A)
s–1
B)
s–1
C)
s–1
D)
s–1
E)
s–1
129. Which of the following statements best describes the condition(s) needed for a successful
formation of a product according to the collision model?
A)
The collision must involve a sufficient amount of energy, provided from the
motion of the particles, to overcome the activation energy.
B)
The relative orientation of the particles has little or no effect on the formation of
the product.
C)
The relative orientation of the particles has an effect only if the kinetic energy of
the particles is below some minimum value.
D)
The relative orientation of the particles must allow for formation of the new bonds
in the product.
6.6 104
1.3 101
9.4 103
3.3 104
2.7 105
2.1 10−2
4.5 10−4
2.2 103
6.0 10−3
1.6 10−3
E)
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.
130. The rate constant for a reaction is 1.5 10–2 s–1 at 734 K and 3.9 10–2 s–1 at 878 K. What is
the activation energy?
A)
15 kJ/mol
B)
36 kJ/mol
C)
440 kJ/mol
D)
4300 kJ/mol
E)
This can’t be solved without knowing the frequency factor.
131. For the second-order reaction NO(g) + O3(g) → NO2(g) + O2(g), the rate constant has been
measured to be 1.08 107 M–1 s–1 at 298 K and the activation energy has been measured to
be 11.4 kJ/mol over the temperature range 195 K to 304 K. What is the rate constant at
233 K? (R = 8.3145 J K–1 mol–1)
A)
M–1 s–1
B)
M–1 s–1
C)
M–1 s–1
D)
M–1 s–1
E)
M–1 s–1
132. The reaction 2H2O2 → 2H2O + O2 has the following mechanism:
H2O2 + I– → H2O + IO–
H2O2 + IO– → H2O + O2 + I–
The catalyst in the reaction is:
A)
H2O
B)
I–
C)
H2O2
D)
IO–
E)
There is no catalyst in this reaction.
133. Which of the following statements is typically true for a catalyst?
1.08 107
1.08 109
2.99 106
3.90 107
9.51 105
I.
The concentration of the catalyst will go down as a reaction proceeds.
II.
The catalyst provides a new pathway in the reaction mechanism.
III.
The catalyst speeds up the reaction.
A)
I only
B)
II only
C)
III only
D)
I and III
E)
II and III
134. The catalyzed pathway in a reaction mechanism has a __________ activation energy and
thus causes a __________ reaction rate.
A)
higher, lower
B)
higher, higher
C)
lower, higher
D)
lower, steady
E)
higher, steady
135. Which of the following statements about enzymes is incorrect?
A)
They are proteins that catalyze specific biologic reactions.
B)
Several hundred are now known.
C)
The molecules they react with are called substrates.
D)
They are equal to inorganic catalysts in efficiency.
E)
All of these are correct.
136. Determine (a) the rate equation and (b) the rate constant for the hypothetical reaction
A + B → C given the following initial concentrations and initial rate data.
[A]0
[B]0
Initial Rate
Run #
(mol/L)
(mol/L)
(mol/L·s)
(1)
0.100
0.100
0.18
(2)
0.100
0.200
0.36
(3)
0.200
0.200
1.44
137. What is the rate law for this reaction?
138. What is the value of the rate constant?
139. How many seconds would it take for the total pressure to be 0.7133 atm?
140. The half-life is constant.
141. A plot of [A] vs. t is a straight line.
142. [A] is constant.
143. The rate is constant over time.
