CHE 107 - HOUR EXAMINATION III - 6 April
1995
University of Kentucky - Department of Chemistry
1. For the reaction
2 C6H12 ---> C12H10 + 7 H2
hydrogen is being generated at a rate of 1.0 M/s. What is the rate
of the reaction?
A. 0.14 M/s
B. 0.29 M/s
C. 1.0 M/s
D. 7.0 M/s
2. A certain reaction
2 A + B + C ---> 3 D
has the rate law: Rate = k[A]0[B]2[C]. The overall order of the
reaction is
A. 0
B. 1
C. 2
D. 3
3. If a reaction is first order, the units of the rate constant are
A. mol L-1 s-1
B. L mol-1 s-1
C. L2 mol-2 s-1
D. s-1
4. For the reaction
2 A + B ---> C + D
the rate law is found to be: Rate = k[A]2[B]. Which of the following
statements is false?
A. The reaction is third order.
B. The order is determined by experimentation only.
C. k is the rate of the reaction.
D. When the concentration of B is doubled as [A] is held constant,
the rate is doubled.
5. For the reaction
A ---> B + C
the plot of 1/[A] vs t is linear. Which of the following is a
false statement?
A. The reaction is first order.
B. The slope of the graph is positive.
C. k = slope.
D. Rate = k[A]2
6. For the reaction,
2 Hg2+(aq) + C2O42-(aq) ---> 2 CO2(aq) + Hg22+,
determine the rate expression consistent with the following data:
[Hg2+]0, M [C2O42-]0, M initial rate, M/s
---------- ------------ -----------------
0.10 0.10 1.2 x 10-7
0.10 0.20 4.8 x 10-7
0.20 0.20 9.6 x 10-7
A. Rate = k[Hg2+]2[C2O42-]2
B. Rate = k[C2O42-][Hg2+]
C. Rate = 2k[C2O42-] + k[Hg2+]
D. Rate = k[Hg2+][C2O42-]2
7. A first order reaction has a half-life of 110 minutes. How long
will it take until only 15.0% of the original amount of the reactant
remains?
A. 25.8 min
B. 129 min
C. 301 min
D. 733 min
8. For the reaction
A ---> C + D,
the plot of ln [A] vs time (in s) gives a straight line with slope
of -0.200. Which statement is true?
A. Rate = k[A]2.
B. The half life is 3.46 s.
C. The rate constant is 20.0 s.
D. Both A and B are true.
9. The activation energy for a reaction can be determined from the
slope of a plot of
A. ln [A] vs ln K
B. k vs T
C. ln [A] vs 1/T
D. ln k vs 1/T
10. A reaction rate doubles as the temperature of a reaction is raised
from 35oC to 50oC. What is the activation energy of the
reaction?
A. 0.672 kJ/mol
B. 8.70 x 10-4 J/mol
C. 38.2 kJ/mol
D. 59.1 kJ/mol
11. For the reaction mechanism:
2 NO ---> N2O2
N2O2 + H2 ---> N2O + H2O
N2O + H2 ---> N2 + H2O
The intermediates in the reaction are:
A. NO and N2
B. H2 and N2O2
C. N2O2 and N2O
D. N2 and H2O
12. For the reaction
2 NO2 + O3 ---> N2O5 + O2
a proposed mechanism is
NO2 + O3 ---> NO3 + O2 fast
NO3 + NO2 ---> N2O5 slow
Which one of the following statements is false?
A. O3 is a catalyst.
B. NO3 is an intermediate.
C. O2 is not an intermediate.
D. The second step is rate determining.
13. Ozone, O3, decomposes according to the following mechanism:
k1
O3 ---> O2 + O
k2
O + O3 ---> 2 O2
Assuming k2 > > k1, the rate law is:
A. rate = k1[O3]
B. rate = k1[O3][O]
C. rate = k2[O3]
D. rate = k2[O][O3]
14. Which one of the following oxidation state assignments for Br
is incorrect?
A. BrO3-, Br, +5
B. BrF3, Br, +3
C. HOBr, Br, -1
D. CaBr2, Br, -1
15. The following reaction occurs in acidic solution
MnO4- + ClO2- ---> MnO2 + ClO4-
Balance the equation above and add all of the coefficients in the
balanced equation. The sum of these coefficients is
A. 23
B. 20
C. 22
D. 19
16. The anode in an electrochemical cell is always
A. the site at which oxidation occurs.
B. connected to a salt bridge.
C. the electrode toward which cations migrate.
D. the electrode toward which electrons flow in the external
circuit.
17. Consider a voltaic cell for which the overall cell reaction is
Co(s) + 2 Fe3+(aq) ---> Co2+(aq) + 2 Fe2+(aq)
The cathode of this cell is
A. a standard hydrogen electrode.
B. a piece of Fe3+.
C. an inert electrode.
D. a piece of cobalt metal.
18. Which statement is true?
A. A strong oxidizing agent has a high, positive reduction potential.
B. A strong reducing agent has a high, positive reduction potential.
C. Electrolysis is a spontaneous reaction.
D. Reduction occurs at the anode.
19. Determine Eo for the following cell using the attached reduction
potentials.
2 Ag(s) + Br2(l) ---> 2 Ag+(aq) + 2 Br-(aq)
A. 1.87 V
B. 0.27 V
C. 2.67 V
D. -0.53 V
20. Consider the reaction below, which is not yet balanced:
Fe(s) + Cu2+(aq) ---> Fe3+(aq) + Cu(s)
What value of n should be used if delta G is to be calculated from
E? (Assume all stoichiometric coefficients are integers).
A. 1
B. 2
C. 3
D. 6
21. What is delta Go for the voltaic cell having the following half
reactions?
Ni2+(aq) + 2 e ---> Ni(s) Eo = -0.25 V
Cl2g) + 2 e ---> 2 Cl-(aq) Eo = 1.36 V
A. -311 kJ
B. +155 kJ
C. -214 kJ
D. -158 kJ
22. Calculate E for the following reaction at 25oC,
Co(s) + Fe2+(aq) ---> Co2+(aq) + Fe(s)
given that [Co2+] = 0.15 M, [Fe2+] = 0.68 M, and Eo = -0.16 V.
A. -0.12 V
B. -0.14 V
C. -0.16 V
D. -0.18 V
23. The passage of an electric current through an electrolyte, causing
an otherwise nonspontaneous oxidation reduction reaction to occur
A. is electrolysis.
B. is a commercial battery.
C. forms products by consumption of electricity.
D. both A and C.
24. Magnesium is used in the cathodic protection of iron because
A. iron is a more reactive metal than is magnesium.
B. magnesium is a better reducing agent than iron.
C. iron has a greater tendency to undergo oxidation than does
magnesium.
D. the two metals form an alloy.
25. How many grams of copper metal can be produced at the cathode of
an electrolytic cell by passing a constant current of 10.0 amperes
through an aqueous copper(II) sulfate solution for 168.0 hours?
A. 9.95 x 101 g
B. 1.99 x 103 g
C. 3.98 x 103 g
D. 5.38 x 104 g
5 January 1996