Download February 13, 2008

CHEM 188 – Spring, 2008
Hour Exam 1 (Early)
February 13, 2008
Instructions:
Your scantron answer sheet must show your NAME, 7-DIGIT KU ID NUMBER, and LAB
SECTION. (Begin these entries at the LEFT end of the space provided.)
In answering the questions, be careful to fill in the corresponding circles on the answer sheet
according to the number of the question on the exam. USE A SOFT (No. 2) PENCIL.

Useful information:
Gas constant,
R = 8.314 J/K  mol
= 0.08206 L  atm/K  mol
Integrated Rate Laws:
Zero - order :
First - order :
Second  order :
Arrhenius equation:
k  Ae -E a /RT
ln
Relation of KP to KC:
1.
[A]  [A]0 - kt
[A]  [A]0 e kt
1
1

 kt
[A] [A]0
k1
Ea  T1  T2


k2
R 
 T1T2




KP = KC(RT)n
For the reaction
4NO2(g) + O2(g)  2N2O5(g)
the rate of loss of molecular oxygen, -d[O2]/dt is 0.024 M/s at a particular time during the
reaction. What is the rate, d[N2O5]/dt, at which N2O5 is being formed?
A. 0.012 M/s
B. 0.024 M/s
C. 0.036 M/s
D. 0.048 M/s
E. none of these
1
2.
For the overall chemical equation, which one of the following can you rightly assume?
2H2S(g) + O2(g)  2S(s) + 2H2O(l)
A.
B.
C.
D.
E.
3.
The reaction is third-order overall.
The reaction is second-order overall.
The rate law is, rate = k[H2S][O2]
The rate law is, rate = k[H2S]2[O2]
The rate law cannot be determined from the information given.
The reaction of peroxydisulfate ion (S2O82) with iodide ion (I) is
S2O82 (aq) + 3 I (aq)  2SO42(aq) + I3(aq)
From the following data collected at a certain temperature, determine the rate law.
Expt. #
[S2O82]0 (M)
[I]0 (M)
Initial rate (M/s)

1
0.080
0.034
2.2 x 10 4
2
0.080
0.017
1.1 x 10 4
3
0.16
0.017
2.2 x 10 4
A. rate = k[S2O82]
B. rate = k[S2O82]2
C. rate = k[S2O82][ I]
D. rate = k[S2O82]2[I]
E. rate = k[S2O82]2[I]2
4.
The reaction of nitric oxide with hydrogen
2NO(g) + 2H2(g)  N2(g) + 2H2O
is second-order in [NO] and first-order in [H2]. At 1280oC, the reaction rate was found to be
1.0 x 10 4 M/s when the NO concentration was 0.010 M and the H2 concentration was 0.040
M. What is the value of the rate constant in units of M 2s 1 at this temperature?
A. 2.5
5.
B. 10
D. 100
E. 250
If concentration is expressed in units of molecules per cubic centimeter (molec/cm3) and time
in units of seconds (s), the units of a second-order rate constant are
A. cm3 molec 1 s 1
D. s  2
6.
C. 25
B. cm6 molec 2 s 1
C. s  1
E. molec cm 3 s 1
A certain first-order reaction, A  B, has a rate constant of 7.6 x 10 3 s 1. The time required
for the reaction to be 60% complete is
A. 0.0038 s
B. 0.69 s
C. 68 s
D. 120 s
E. 300 s
2
7.
At 25oC, the second-order reaction
NOCl(g)  NO(g) + ½ Cl2(g)
is 50% complete after 5.82 hours when the initial concentration of NOCl is 4.46 M. What is
the value of the rate constant (in units of M1hr1) for this reaction?
A. 0.039
8.
B. 0.077
C. 0.17
D. 1.3
E. 2.6
The chemical reaction A  products is known to have a rate law of the general type
rate = k[A]n.
A plot of 1/[A] versus time was found to give a straight line with a positive slope. What is n,
the order of reaction?
A. zero
9.
E. none of these
B. 10 min
C. 20 min
D. 40 min
E. 80 min
B. 53
C. 72
D. 85
E. 107
When the concentrations of reactant molecules are increased, the rate of reaction increases.
The best explanation is: As the reactant concentrations increase, …
A.
B.
C.
D.
E.
12.
D. third
For a certain reaction, the rate constant, k, at 35oC is twice the value of the rate constant at
25oC. What is the activation energy, Ea, for this reaction in units of kJ/mol?
A. 31
11.
C. second
A certain reaction, A  products, is zero-order in [A]. At 25oC, it was found that 20 minutes
were required for the concentration of A to decrease from 2.0 M to 1.0 M. At this temperature,
how much time would be required for [A] to decrease from 1.0 M to 0.50 M?
A. 5.0 min
10.
B. first
the average kinetic energy of the molecules increases.
the frequency of molecular collisions increases.
the rate constant increases.
the activation energy decreases.
the order of the reaction increases.
Identify the reaction intermediate(s) in the following reaction mechanism:
A + B  AB
AB + C  D
DB+E
A. AB
B. B
C. AB and C
D. C
E. AB and D
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13.
For the following reaction
2NaHCO3(s)  Na2CO3(s) + CO2(g) + H2O(g)
which is the correct equilibrium constant expression?
A. Kc = [Na2CO3][CO2][H2O] / [NaHCO3]
B. Kc = [Na2CO3][CO2][H2O] / [NaHCO3]2
C. Kc = [Na2CO3]2CO2][H2O] / [NaHCO3]
D. Kc = [CO2][H2O] / [NaHCO3]
E. Kc = [CO2][H2O]
14.
If the equilibrium constant is K1 for the reaction
HBr(g)  ½ H2(g) + ½ Br2(g)
Then for the reaction
H2(g) + Br2(g)  2HBr(g)
the equilibrium constant K2 must be equal to:
A. K2 = 2K1
B. K2 = K12
C. K2 = 1/K1
D. K2 = 1/(2K1)
E. K2 = 1/K12
15.
Which of the following is a true statement about chemical equilibrium in general?
A. At equilibrium, the total concentration of products equals the total concentration of reactants
B. Equilibrium is the result of the cessation of all chemical change.
C. There is only one set of equilibrium concentrations that equals the Kc value.
D. The rate constant of the forward reaction is equal to the rate constant for the reverse
reaction.
E. At equilibrium, the rate of the forward process is the same as the rate of the reverse process.
16.
At 1000 K, the following is true:
H2(g) + Br2(g)  2HBr(g)
k1 = 5.7 x 105 M 1 s 1
2HBr(g)  H2(g) + Br2(g)
k2 = 1.8 x 103 M 1 s 1
where k1 and k2 are the rate constants for the reactions. What is the equilibrium constant Kc
for the following reaction?
H2(g) + Br2(g)  2HBr(g)
A. 3.2 x 102
B. 3.1 x 103
C. 1.0 x 109
D. 9.7 x 1010
E. none of these
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17.
For the reaction
H2(g) + I2(g)  2HI(g)
Kc = 50.2 at 445oC.
If [H2] = [I2] = 0.100 M and [HI] = 0.750 M at 445oC, which one of the following statements is
true?
A.
B.
C.
D.
E.
18.
The system is at equilibrium; no change will occur.
The concentrations of H2 and I2 will increase as the system approaches equilibrium.
The concentration of HI will rise as the system approaches equilibrium.
The concentrations of H2 and HI will fall as the system approaches equilibrium.
The concentrations of HI and I2 will increase as the system approaches equilibrium.
The equilibrium constant KC for the reaction
2SO3(g)  2SO2(g) + O2(g)
is 3.5 x 10  7 at 350oC. What is the value of KP for this reaction at 350oC?
A. 6.8 x 10  9
19.
B. 1.2 x 10  8
C. 3.5 x 10  7
D. 1.0 x 10  5
E. 1.8 x 10  5
Nitric oxide is converted to nitrogen dioxide by the reaction
2NO(g) + O2(g)  2NO2(g).
In an experiment at 25oC, the concentrations of the reacting species at equilibrium were found
to be [NO] = 0.0542 M, [O2] = 0.127 M, and [NO2] = 15.5 M. Calculate the equilibrium
constant, KC, of the reaction at this temperature.
A. 1.55 x 10 6
20.
B. 4.44 x 10 4
C. 3.15 x 10 2
D. 2.25 x 10 2
E. 6.44 x 10 5
The equilibrium constant, KP, for the decomposition of phosphorus pentachloride
PCl5(g)  PCl3(g) + Cl2(g)
is found to be 1.05 at 250oC. If the equilibrium pressures of PCl5 and PCl3 are 0.875 atm and
0.463 atm, respectively, what is the equilibrium partial pressure of Cl2 at 250oC?
A. 0.278 atm
21.
B. 0.556 atm
C. 0.745 atm
D. 1.34 atm
E. 1.98 atm
1.25 moles of NOCl were placed in a 2.50 L reaction chamber at 427oC. After equilibrium was
reached, 1.10 moles of NOCl remained. Calculate the equilibrium constant Kc for the
reaction:
2NOCl(g)  2NO(g) + Cl2(g)
A. 3.0 x 10  4
B. 5.6 x 10  4
C. 1.4 x 10  3
D. 4.1 x 10  3
E. 1.8 x 103
5
22.
Consider the reaction
N2(g) + O2(g)  2NO(g)
Kc = 0.10 at 2,000oC.
Starting with initial concentrations of 0.10 M of N2 and 0.10 M of O2, calculate the
equilibrium concentration of NO in M.
A. 0.0055 M
B. 0.011 M
D. 0.022 M
23.
C. 0.014 M
E. 0.027 M
The equilibrium constant KC for the reaction
H2(g) + Br2(g)  2HBr(g)
is 2.18 x 106 at 730oC. If 0.50 mole of pure HBr was placed in a 10.0-L reaction vessel at
730oC, what would be the concentration of Br2 at equilibrium?
A. 3.39 x 105 M
B. 6.77 x 105 M
D. 6.67 x 104 M
24.
E. 3.39 x 104 M
In which of the following gas-phase equilibria is the yield of products increased by increasing
the total pressure on the reaction mixture?
A.
B.
C.
D.
E.
25.
C. 2.03 x 105 M
CO(g) + H2O(g)  CO2(g) + H2(g)
PCl5 (g)  PCl3(g) + Cl2(g)
2SO3 (g)  2SO2(g) + O2(g)
2NO(g) + Cl2(g)  2NOCl(g)
None of the above.
The enthalpy change for the reaction 2NO(g)  N2(g) + O2(g) is H =  180 kJ. Which one
of the following statements is true?
A.
B.
C.
D.
E.
Kp at 1000 K is greater than Kp at 2000 K.
Kp at 1000 K is less than Kp at 2000 K.
Kp at 1000 K is the same as Kp at 2000 K.
Kp depends upon total pressure as well as temperature.
None of the above.
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