CHEM 1200
Practice Test 2
Answers
1. For the reaction, C6H14 (g) ®
C6H6 (g) + 4 H2 (g),
DP(C6H14)/D t was found to be -6.2 x 10-3 atm/sec.
Determine the value of DP(H2)/Dt at the same time.
a. 6.2 x 10-3 atm/sec
b. 1.6 x 10-3 atm/sec
c. 2.5 x 10-2 atm/sec
d. - 1.6 x 10-3 atm/sec
e. -2.5 x 10-2 atm/sec
2. The reaction, A + 2 B ® products, was found to have the following rate law: rate = [A][B]2
While holding the concentration of A constant, the concentration of B was increased three fold. Predict by what factor the rate of the reaction will increase.
a. 3
b. 6
c. 9
d. 27
e. 30
3. The units for a first-order rate constant are:
a. M/s
b. 1/M.s
c. 1/s
d. 1/M2.s
4. Nitric oxide reacts with hydrogen to form nitrous oxide and water. Use the following data to determine the rate equation for the reaction.
2 NO + H2 ® N2O + H2O
Expt.# [NO]o [H2]o Initial Rate
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1 0.021 0.065 1.46 M/min
2 0.021 0.260 1.46 M/min
3 0.042 0.065 5.84 M/min
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a. rate = k[NO]
b. rate = k[NO]2
c. rate = k[NO][H2]
d. rate = k[NO]2[H2]
e. rate = k[NO]2[H2]2
5. Ammonium ion (NH4+) reacts with nitrite ion (NO2-) according to the following equation:
NH4+ (aq) + NO2- (aq) ® N2 (g) + 2 H2O (l)
The following initial rates of reaction have been measured for the given reactant concentrations:
Expt.# [NH4+] [NO2-] Rate (M/hr)
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1 0.010 0.020 0.020
2 0.015 0.020 0.030
3 0.010 0.010 0.005
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Which of the following is the rate law (rate equation) for this reaction?
a. rate = [NH4+][NO2-]4
b. rate = [NH4+][NO2-]
c. rate = [NH4+][NO2-]2
d. rate = [NH4+]2[NO2-]
e. rate = [NH4+]1/2[NO2-]1/4
6. An increase in the temperature of the reactants causes an increase in the rate of reaction. The best explanation is: As the temperature increases
a. the concentration of the reactants increases
b. the activation energy decreases
c. the collision frequency increases
d. the activation energy increases
7. Complete the statement: A catalyst
a. increases the activation energy
b. alters the reaction mechanism
c. increases the average kinetic energy of the reactants
d. increases the concentration of reactants
e. increases the collision frequency of reactant molecules
8. Suppose that the reaction: Cl2 (g) + 3 F2 (g) ® 2 ClF3 (g)
is first order in F2 and second order in Cl2. Which of the following is not true?
a. If [F2] is doubled, the rate of the reaction doubles
b. If [Cl2] is doubled, the rate of the reaction increases four fold
c. If both [F2] and [Cl2] are doubled, the rate of the reaction is increased eight fold
d. If [F2] is doubled and [Cl2] is halved, the rate of the reaction remains the same
e. The rate of the reaction is third order overall
9. The equilibrium constant expression for the reaction below is:
2 BrF5 (g) = Br2 (g) + 5 F2 (g)
a. Keq = [Br2][F2]/[BrF5]
b. Keq = [Br2][F2]5/[BrF5]2
c. Keq = [Br2][F2]2/[BrF5]5
d. Keq = [BrF5]2/[Br2][F2]5
e. Keq = [BrF5]5/[Br2][F2]2
10. 1.25 moles of NOCl were placed in a 2.50 L flask at 427oC. After equilibrium was reached 1.10 moles of NOCl remained. Calculate the equilibrium constant Kc for the reaction:
2 NOCl (g) = 2 NO (g) + Cl2 (g)
a. 3.0 x 10-4
b. 1.8 x 103
c. 1.4 x 10-3
d. 5.6 x 10-4
e. 4.1 x 10-3
11. The brown gas NO2 and the colorless gas N2O4 exist in equilibrium:
2 NO2 = N2O4
In an experiment, 0.625 mol of N2O4 was introduced into
a 5.00 L vessel and was allowed to decompose until it reached
equilibrium with NO2. The concentration of N2O4 at
equilibrium was 0.0750 M. The value of Kc for the reaction is:
a. 7.5
b. 0.125
c. 0.0750
d. 0.10
e. 0.050
12. At 400oC, Kc = 64 for the reaction: H2 (g) + I2 (g) = 2 HI (g)
If 3.00 mol of H2 and 3.00 mol of I2 are introduced into an empty 4.0 L vessel, find the equilibrium concentration of HI at 400oC.
a. 0.15
b. 1.2
c. 2.4
d. 4.8
e. 5.8
13. At 700 K, the reaction: 2 SO2 (g) + O2 ® 2 SO3 (g)
has an equilibrium constant Kc = 4.3 x 106, and the following concentrations are present:
[SO2] = 0.010 M [SO3] = 10 M [O2] = 0.010 M
Is the mixture at equilibrium, yes or no? If not at equilibrium, in which direction, left to right, or right to left, will reaction occur to reach equilibrium?
a. yes
b. no, left to right
c. no, right to left
d. there is not enough information to tell
14. For the following reaction at equilibrium, which one of the changes below would cause the equilibrium to shift to the left?
2 NOBr (g) ® 2 NO (g) + Br2 (g) DHo = 30 kJ
a. increase the container volume
b. remove some NO
c. remove some Br2
d. add more NOBr
e. decrease the temperature
15. Consider the following equilibrium system:
PCl5 = PCl3 + Cl2 DHo = +87.8 kJ
Which of the following statements is false?
a. Increasing the concentration of PCl5 causes the system to reach an equilibrium that has more product
b. Increasing the temperature shifts the equilibrium to the right
c. A catalyst speeds up the approach to equilibrium and shifts the position of equilibrium to the left
d. When the total pressure of the system is decreased, the equilibrium is shifted to the right
e. Increasing the temperature causes the equilibrium constant to increase
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