Chapter 6 Kinetics Review Questions
1) At elevated temperatures, methylisonitrile (CH3NC) isomerizes to acetonitrile (CH3CN):
CH3NC (g) → CH3CN (g)
At the start of the experiment, there are 0.200 mol of reactant (CH3NC) and 0 mol of product (CH3CN) in the
reaction vessel. After 25 min of reaction, 0.108 mol of reactant (CH3NC) remain. The average rate of
decomposition of methyl isonitrile, CH3NC, in this 25 min period is __________ mol/min.
A) 3.7 × 10-3
B) 0.092
C) 2.3
D) 4.3 × 10-3
E) 0.54
2) A reaction was found to be second order in carbon monoxide concentration. The rate of the reaction
__________ if the [CO] is doubled, with everything else kept the same.
A) doubles
B) remains unchanged
C) triples
D) increases by a factor of 4
E) is reduced by a factor of 2.
3) The overall order of a reaction is 2. The units of the rate constant for the reaction are __________.
A) M/s
B) M-1s-1
C) 1/s
D) 1/M
E) s/M 2
4) The half-life of a first-order reaction is 13 min. If the initial concentration of reactant is 0.085 M, it takes
________min for it to decrease to 0.055 M.
A) 8.2
B) 11
C) 3.6
D) 0.048
E) 8.4
5) A second-order reaction has a half-life of 18 s when the initial concentration of reactant is 0.71 M. The rate
constant for this reaction is __________ M-1s-1 .
A) 7.8 × 10-2
B) 3.8 × 10-2
C) 2.0 × 10-2
D) 1.3
E) 18
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6) One difference between first- and second-order reactions is that __________.
A) the half-life of a first-order reaction does not depend on [A]0 ; the half-life of a second-order reaction does
depend on [A]0
B) the rate of a first-order reaction does not depend on reactant concentrations; the rate of a second-order
reaction does depend on reactant concentrations
C) the rate of a first-order reaction depends on reactant concentrations; the rate of a second-order reaction does
not depend on reactant concentrations
D) a first-order reaction can be catalyzed; a second-order reaction cannot be catalyzed
E) the half-life of a first-order reaction depends on [A]0 ; the half-life of a second-order reaction does not depend
on [A]0
7) In general, as temperature goes up, reaction rate __________.
A) goes up if the reaction is exothermic
B) goes up if the reaction is endothermic
C) goes up regardless of whether the reaction is exothermic or endothermic
D) stays the same regardless of whether the reaction is exothermic or endothermic
E) stays the same if the reaction is first order
8) For the elementary reaction
NO3 + CO  NO2 + CO2
the molecularity of the reaction is __________, and the rate law is rate = __________.
A) 2, k[NO3 ][CO]
B) 4, k[NO3 ][CO][NO2 ][CO2 ]
C) 2, k[NO2 ][CO2 ]
D) 2, k[NO3 ][CO]/[NO2 ][CO2 ]
E) 4, k[NO2 ][CO2 ]/[NO3 ][CO]
9) SO2Cl2 decomposes in the gas phase by the reaction
SO2 Cl2 (g)  SO2 (g) + Cl2 (g)
The reaction is first order in SO2Cl2 and the rate constant is 3.0 × 10-6s-1 at 600 K. A vessel is charged with
3.3 atm of SO2Cl2 at 600 K. The partial pressure of SO 2 at 3.0  105s is __________ atm.
A) 2.1
B) 2.0
C) 1.3
D) 3.0
E) 3.7
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10) At elevated temperatures, methylisonitrile (CH3NC) isomerizes to acetonitrile (CH3CN):
CH3NC (g) → CH3CN (g)
The dependence of the rate constant on temperature is studied and the graph below is prepared from the results.
The energy of activation of this reaction is __________ kJ/mol.
A) 160
B) 1.6 × 105
C) 4.4 × 10-7
D) 4.4 × 10-4
E) 1.9 × 104
11) A particular first-order reaction has a rate constant of 1.35 × 102s-1 at 25°C. What is the magnitude of k at
95°C if Ea = 55.5 kJ/mol?
A) 9.60 × 103
B) 2.85 × 104
C) 576
D) 4.33 × 1087
E) 1.36 × 102
12) Which of the quantities in the enthalpy level diagram below is (are) affected by the use of a catalyst?
Enthalpy
I
II
III
A.
I only
C.
III only
B.
I and II only
D.
II and III only
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Free Response Questions
1) How could you, by graphing two variables, prove a reactions is (a) first order (b) second order
(What would you have to graph, and what would the
graph look like? )
2) The reaction NO2  NO + ½ O2 has the rate constant k = 0.63 M-1s-1 at 25oC.
(i) Based on the units for k, is the reaction zero-, first-, or second-order in NO2?
(ii) If the initial concentration of NO2 is 0.100 M, how long would it take for the concentration to
decrease to 0.025 M?
(iii)What is the half-life time, in seconds, for NO2?
(iv) What is the rate of the same reaction when the temperature is increased to 45oC? Ea = 68 kJ/mol
(v) Does your answer from (iv) seem reasonable based on your knowledge of how changing
temperature effects the rate of a reaction?
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3) The energy of activation for a hypothetical reaction:
A + B  C is 345 kJ/mol for the uncatalyzed reaction and
Is 165 kJ/mol for the reaction catalyzed on a metal surface.
E for this reaction is 90 kJ/mol of reaction. Draw and label a reaction
coordinate diagram.
3)
The data obtained for the reaction:
2 NO(g) + O2(g)  2 NO2(g)
Data
[NO]
[O2]
Run 1
Run 2
Run 3
Run 4
0.20 M
0.20
0.40
0.10
0.20 M
0.40
0.40
0.10
Initial rate: mol L-1
sec-1
4.64x10-8
9.28x10-8
3.71x10-7
5.80x10-9
a) What is the rate law equation for the reaction?
b) What is the value of the rate law constant, including units?
c) The following mechanism has been suggested:
1. NO(g) + O2(g)  NO3(g) (Equilibrium)
2. NO3(g) + NO(g)  2 NO2(g) (Slow)
i) Show that this mechanism leads to the observed rate equation.
ii) Identify any intermediate(s) in the above mechanism.
iii) Identify any catalyst(s) in the above mechanism.
d) The reaction rate is increased five-fold (5 times) when the temperature is increased from
1400 K to 1500 K. What is the energy of activation for the reaction?
e) Explain why the following mechanism is not consistent with the rate expression.
NO (g) + O2 (g) → NO2(g) + O (g); slow step
NO (g) + O (g) → NO2 (g); fast step
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