CHM 2046C Module Nine
Koth 5th Edition Chapter 15
Sample Multiple Choice #1 Answers
1. The rate of a chemical reaction usually varies with
1.concentration.
2.time.
3.temperature.
4.catalyst.
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a. |
1 only |
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b. |
1 and 3 only |
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c. |
3 and 4 only |
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d. |
1, 3, and 4 |
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e. |
1, 2, 3, and 4 |
2. For the reaction, I + I --> I2 at 25?C in CCl4, k = 8.2 x 109 L mol-1s-1. This reaction is
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a. |
first order. |
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b. |
second order. |
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c. |
endothermic. |
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d. |
can't tell without knowing the activation energy. |
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e. |
can't tell without an experiment showing the
concentration dependence of the iodine atom. |
3. Which equation describes the relationship between the
rates at which Cl2 is consumed and ClF3 is produced in
the following reaction:
Cl2(g) + 3F2(g) --> 2ClF3(g)
|
a. |
-d[Cl2]/dt = -d[ClF3]/dt |
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b. |
-d[Cl2]/dt = d[ClF3]/dt |
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c. |
-d[Cl2]/dt = 2[-d[ClF3]/dt] |
|
d. |
2[-d[Cl2]/dt] = -d[ClF3]/dt |
|
e. |
2[-d[Cl2]/dt] = d[ClF3]/dt |
4. For a certain reaction, the rate expression is given by
the equation below:
Rate = k [X]3/2[Y]1/2
The rate has the
units 
.
Which of the following are possible units for the rate constant, k?
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a. |
|
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b. |
|
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c. |
|
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d. |
|
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e. |
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5. The rate law for the chemical
reaction, 5Br- + BrO3- + 6H+ -->
3Br2 + 3H2O has been determined experimentally to be
The reaction order with respect to the hydrogen ion is
|
a. |
1. |
|
b. |
2. |
|
c. |
6. |
|
d. |
k[H+]2. |
|
e. |
k[Br-][BrO3-][H+]2 |
6. The
correct answer is:
addition of 200 cm3 of 1.0 M
HCl instead of 100 cm3.
Explanation:
The concentration of HCl is the same in option
(b) as it is in the original problem so the addition of more HCl which is
already in excess will not increase the rate.
Solution Reference:
Page 694, The Effect of Concentration on
Reaction Rate
7. The
correct answer is:
The rate of a catalyzed reaction is
dependent upon the concentration of the catalyst.
Explanation:
Let us look at some of the distractors.
a. Each reaction has its own characteristic activation
energy.
b. A reaction can be zero order in a reactant.
d. The value of a specific rate constant is independent of the concentrations
of the reacting species.
e. The rate law must be determined experimentally.
Solution Reference:
Page 692, Reaction Conditions and Rate and
Page 710, A Microscopic View of Reaction Rates.
8. The
correct answer is:
a large DH or DE
value.
Explanation:
DH and DE give information on the heat
content of the reaction not on the rate of the reaction.
Solution Reference:
Page 687, Chemical Kinetics and Page 710, A
Microscopic View of Reaction Rates
9. The
correct answer is:
Vessel one requires the same amount of
time as vessel two.
Explanation:
For first order reactions, the time required
for half of the reactant to react is a constant and it is called a half-life.
Solution Reference:
Page 707, Half-Life and First-Order Reactions
10. The
correct answer is:
30 min.
Explanation:
By decreasing the "original amount"
by half for each half-life, we can see that there are five half-lifes.
Solution Reference:
Page 707, Half-Life and First-Order Reactions
11. The
correct answer is:
25.3 sec
Explanation:
Solution Reference:
Page 707, Half-Life and First-Order Reactions
12. The
correct answer is:
2.
Explanation:
Solution Reference:
Page 697, Determination of the Rate Equation
Question Instructions: The
stoichiometric equation for the reaction of nitric oxide with oxygen is 2NO + O2
--> 2NO2. The data below were obtained at 273°C.
13. The correct answer is:
2
Explanation:
Compare Experiments IV and III. When the
concentration of O2 is doubled, the rate is doubled. The rate of the
reaction is therefore first order in oxygen.
Solution Reference:
Page 697, Determination of the Rate Equation
Question Instructions: The
stoichiometric equation for the reaction of nitric oxide with oxygen is 2NO + O2
--> 2NO2. The data below were obtained at 273°C.
14. The
correct answer is:
16
Explanation:
Compare Experiments IV and II. When the
concentration of NO is doubled and the concentration of O2 is held
constant, the rate is quadrupled. Therefore, the rate dependence of NO is to
the second power. Therefore, 
Solution Reference:
Page 697, Determination of the Rate Equation
Question Instructions: The
stoichiometric equation for the reaction of nitric oxide with oxygen is 2NO + O2
--> 2NO2. The data below were obtained at 273°C.
15. The correct answer is:
k[NO]2[O2]
Explanation:
The reaction is second order in NO and first
order in O2.
Solution Reference:
Page 697, Determination of the Rate Equation
Question Instructions: Two
reactants, A and B, are mixed and the reaction is timed until a color change
occurs. The data are:
16. The
correct answer is:
1.
Explanation:
A time is given and time is not a rate. The
rate is proportional to 1/time, so the more rapid the rate the shorter the
time. Consider the first two sets of data (when the concentration of B is the
same). When the concentration of A is doubled, the time is halved so the
reaction must be first order with respect to A.
Solution Reference:
Page 697, Determination of the Rate Equation
Question Instructions: Two
reactants, A and B, are mixed and the reaction is timed until a color change
occurs. The data are:
17. The
correct answer is:
2.
Explanation:
See the response to 16. Compare the first and
third sets of data. When the concentration of [B] is doubled, it takes 1/4 the
time for the color change.
Solution Reference:
Page 697, Determination of the Rate Equation
18. The
correct answer is:
Solution Reference:
Page 703, Second-Order Reactions
19. The
correct answer is:
1000 s
Explanation:
Solution Reference:
Page 703, Second-Order Reactions
20. The
correct answer is:
adding a catalyst.
Explanation:
The purpose of a catalyst is to provide
another pathway for a reaction. This means that there is a different barrier
and that the activation energy would be different.
Solution Reference:
Page 718, Effect of Catalysts on Reaction Rate
21. The
correct answer is:
ln k vs. 1/T.
Explanation:
The latter equation is of the form of a linear equation, y = b + mx. When ln k
is plotted against 1/T, there will be a straight line.
Solution Reference:
Page 715, The Arrhenius Equation
22. The
correct answer is:
210 kJ.
Explanation:
DH reaction = Eaf - Ear
-200 kJ = 10 kJ - Ear
Ear = 210 kJ
Solution Reference:
Page 718, The Effect of Catalysts on Reaction
Rate
23. The
correct answer is:
In a series of stepwise reactions, the
rate-determining step is the fast one.
Explanation:
The rate-determining step is the slowest step
(or slowest reaction in the reaction sequence).
Solution Reference:
Page 724, Reaction Mechanisms
Question Instructions: A
suggested mechanism for the decomposition of ozone is:
24. The correct answer is:
Explanation:
Use the rapid equilibrium step and solve for
the [O] concentration.
The rate of the reaction depends upon the rate of the slow step. Rate = k[O][O3].
We would like to eliminate any intermediates from the experimental rate law and
try to obtain a rate law in terms of the reactants. Combining the two equations
above by eliminating [O], we get
Solution Reference:
Page 724, Reaction Mechanisms
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Question Instructions: A
suggested mechanism for the decomposition of ozone is:
25. The correct answer is:
decrease.
Explanation:
One solves this question by using the
experimental rate law from question 24. Since O2 is in the
denominator, increasing the O2 concentration would decrease the rate
of the reaction.
Solution Reference:
Page 724, Reaction Mechanisms