Download Practice Problems Exam 2 1312

Chemical Kinetics
1) A burning splint will burn more vigorously in pure oxygen than in air because
A) oxygen is a reactant in combustion and concentration of oxygen is higher in pure oxygen than is in air.
B) oxygen is a catalyst for combustion.
C) oxygen is a product of combustion.
D) nitrogen is a product of combustion and the system reaches equilibrium at a lower temperature.
E) nitrogen is a reactant in combustion and its low concentration in pure oxygen catalyzes the combustion.
2) Of the following, all are valid units for a reaction rate except __________.
A) mol/L
B) M/s
C) mol/hr
D) g/s
E) mol/L-hr
3) Nitrogen dioxide decomposes to nitric oxide and oxygen via the reaction:
2NO2 → 2NO + O2
In a particular experiment at 300 °C, [NO2] drops from 0.0100 to 0.00650 M in 100 s. The rate of
disappearance of NO2 for this period is __________ M/s.
A) 0.35
B) 3.5 × 10-3
C) 3.5 × 10-5
D) 7.0 × 10-3
E) 1.8 × 10-3
4) At elevated temperatures, dinitrogen pentoxide decomposes to nitrogen dioxide and oxygen:
2N2O5(g) → 4NO2 (g) + O2 (g)
When the rate of formation of O2 is 2.2 × 10-4 M/s, the rate of decomposition of N2O5 is __________ M/s.
A) 1.1 × 10-4
B) 2.2 × 10-4
C) 2.8 × 10-4
D) 4.4 × 10-4
E) 5.5 × 10-4
5) Which one of the following is not a valid expression for the rate of the reaction below?
4NH3 + 7O2 → 4NO2 + 6H2O
1 Δ O2 
7
Δt
1 Δ  NO2 
A) 
B)
4
Δt
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1 Δ  H 2O
6
Δt
1 Δ  NH3 
D) 
4
Δt
E) All of the above are valid expressions of the reaction rate.
C)
6) Of the units below, __________ are appropriate for a first-order reaction rate constant.
A) M s-1
B) s-1
C) mol/L
D) M-1 s-1
E) L mol-1 s-1
7) The rate law of a reaction is rate = k[D][X]. The units of the rate constant are __________.
A) mol L-1s-1
B) L mol-1s-1
C) mol2 L-2s-1
D) mol L-1s-2
E) L2 mol -2s-1
The data in the table below were obtained for the reaction:
A + B → P
The data in the table below were obtained for the reaction:
2 ClO2 (aq) + 2 OH- (aq) → ClO3- (aq) + ClO2- (aq) + H2O (1)
8) What is the order of the reaction with respect to ClO2?
A) 1
B) 0
C) 2
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D) 3
E) 4
9) What is the order of the reaction with respect to OH-?
A) 0
B) 1
C) 2
D) 3
E) 4
10) What is the overall order of the reaction?
A) 4
B) 0
C) 1
D) 2
E) 3
11) What is the magnitude of the rate constant for the reaction?
A) 1.15 × 104
B) 4.6
C) 230
D) 115
E) 713
12) The rate law for a reaction is
rate = k [A][B]2
Which one of the following statements is false?
A) The reaction is first order in A.
B) The reaction is second order in B.
C) The reaction is second order overall.
D) k is the reaction rate constant
E) If [B] is doubled, the reaction rate will increase by a factor of 4.
13) Under constant conditions, the half-life of a first-order reaction __________.
A) is the time necessary for the reactant concentration to drop to half its original value
B) is constant
C) can be calculated from the reaction rate constant
D) does not depend on the initial reactant concentration
E) All of the above are correct.
14) The reaction
2NO2 → 2NO + O2
follows second-order kinetics. At 300°C, [NO2] drops from 0.0100 M to 0.00650 M in 100.0 s. The rate
constant for the reaction is __________ M-1s-1.
A) 0.096
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B) 0.65
C) 0.81
D) 1.2
E) 0.54
15) The reaction
CH3-N≡C → CH3-C≡N
is a first-order reaction. At 230.3 °C, k = 6.29 × 10-4s-1. If [CH3 N C] is 1.00 × 10-3 initially, [CH3 N C]
is __________ after 1.000 × 103 s.
A) 5.33 × 10-4
B) 2.34 × 10-4
C) 1.88 × 10-3
D) 4.27 × 10-3
E) 1.00 × 10-6
16) Which one of the following graphs shows the correct relationship between concentration and time for a
reaction that is second order in [A]?
A)
B)
C)
D)
E)
17) The following reaction is second order in [A] and the rate constant is 0.039 M-1s-1:
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A → B
The concentration of A was 0.30 M at 23 s. The initial concentration of A was __________ M.
A) 2.4
B) 0.27
C) 0.41
D) 3.7
E) 1.2 × 10-2
18) The following reaction is second order in [A] and the rate constant is 0.025 M-1s-1:
A → B
The concentration of A was 0.65 M at 33 s. The initial concentration of A was __________ M.
A) 2.4
B) 0.27
C) 0.24
D) 1.4
E) 1.2 × 10-2
The reaction A → B is first order in [A]. Consider the following data.
19) The rate constant for this reaction is __________ s-1.
A) 0.013
B) 0.030
C) 0.14
D) 3.0
E) 3.1 × 10-3
20) The half-life of this reaction is __________ s.
A) 0.97
B) 7.1
C) 5.0
D) 3.0
E) 0.14
The reaction A → B is first order in [A]. Consider the following data.
21) The rate constant for this reaction is __________ s-1.
A) 6.9 × 10-2
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B) 3.0 × 10-2
C) 14
D) 0.46
E) 4.0 × 102
22) The concentration of A is __________ M after 40.0 s.
A) 1.3 × 10-2
B) 1.2
C) 0.17
D) 3.5 × 10-4
E) 0.025
23) The rate constant of a first-order process that has a half-life of 225 s is __________ s-1.
A) 0.693
B) 3.08 × 10-3
C) 1.25
D) 12.5
E) 4.44 × 10-3
24) The rate constant of a first-order process that has a half-life of 3.50 min is __________ s-1.
A) 0.693
B) 1.65 × 10-2
C) 1.98
D) .198
E) 3.30 × 10-3
25) The reaction A (aq) → B (aq) is first order in [A]. A solution is prepared with [A] = 1.22 M. The
following data are obtained as the reaction proceeds:
The rate constant for this reaction is __________ s-1.
A) 0.23
B) 1.0
C) 0.17
D) 0.12
E) -0.12
26) 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 both first-order and second-order reactions do not 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) None of the above are true.
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27) At elevated temperatures, methylisonitrile (CH3NC) isomerizes to acetonitrile (CH3CN):
CH3NC (g) → CH3CN (g)
The reaction is first order in methylisonitrile. The attached graph shows data for the reaction obtained at
198.9°C.
The rate constant for the reaction is __________ s-1.
A) -1.9 × 104
B) +1.9 × 104
C) -5.2 × 10-5
D) +5.2 × 10-5
E) +6.2
28) The decomposition of N2O5 in solution in carbon tetrachloride proceeds via the reaction
2N2O5 (soln) → 4NO2 (soln) + O2 (soln)
The reaction is first order and has a rate constant of 4.82 × 10-3 s-1 at 64°C. The rate law for the reaction is rate
= __________.
A) k[N2O5]2
 NO2  O2 
k
2
 N 2 O5 
4
B)
C) k[N2O5]
 N 2 O5 
k
4
 NO2  O2 
2
D)
E) 2k[N2O5]
29) As the temperature of a reaction is increased, the rate of the reaction increases because the __________.
A) reactant molecules collide less frequently
B) reactant molecules collide more frequently and with greater energy per collision
C) activation energy is lowered
D) reactant molecules collide less frequently and with greater energy per collision
E) reactant molecules collide more frequently with less energy per collision
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30) The rate of a reaction depends on __________.
A) collision frequency
B) collision energy
C) collision orientation
D) all of the above
E) none of the above
31) 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
32) In general, as temperature goes down, reaction rate __________.
A) goes down if the reaction is exothermic
B) goes down if the reaction is endothermic
C) stays the same regardless of whether the reaction is exothermic or endothermic
D) goes down regardless of whether the reaction is exothermic or endothermic
E) none of the above
The intermediate reactant in the reaction is __________.
A) A
B) B
C) C
D) D
E) X
33) 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]
34) Of the following, __________ will lower the activation energy for a reaction.
A) increasing the concentrations of reactants
B) raising the temperature of the reaction
C) adding a catalyst for the reaction
D) removing products as the reaction proceeds
E) increasing the pressure
35) The rate law of the overall reaction
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A + B → C
is rate = k[A]2. Which of the following will not increase the rate of the reaction?
A) increasing the concentration of reactant A
B) increasing the concentration of reactant B
C) increasing the temperature of the reaction
D) adding a catalyst for the reaction
E) All of these will increase the rate.
36) A catalyst can increase the rate of a reaction __________.
A) by changing the value of the frequency factor (A)
B) by increasing the overall activation energy (Ea) of the reaction
C) by lowering the activation energy of the reverse reaction
D) by providing an alternative pathway with a lower activation energy
E) All of these are ways that a catalyst might act to increase the rate of reaction.
37) Consider the following reaction:
3A → 2B
The average rate of appearance of B is given by Δ[B]/Δt. Comparing the rate of appearance of B and the rate of
disappearance of A, we get Δ[B]/Δt = __________ × (-Δ[A]/Δt).
A) -2/3
B) +2/3
C) -3/2
D) +1
E) +3/2
38) Which substance in the reaction below either appears or disappears the fastest?
4NH3 + 7O2 → 4NO2 + 6H2O
A) NH3
B) O2
C) NO2
D) H2O
E) The rates of appearance/disappearance are the same for all of these.
39) Consider the following reaction:
A → 2C
The average rate of appearance of C is given by Δ[C]/Δt. Comparing the rate of appearance of C and the rate of
disappearance of A, we get Δ[C]/Δt = __________ × (-Δ[A]/Δt).
A) +2
B) -1
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C) +1
D) +1/2
E) -1/2
A flask is charged with 0.124 mol of A and allowed to react to form B according to the reaction A(g) →B(g).
The following data are obtained for [A] as the reaction proceeds:
40) The average rate of disappearance of A between 10 s and 20 s is __________ mol/s.
A) 2.2 × 10-3
B) 1.1 × 10-3
C) 4.4 × 10-3
D) 454
E) 9.90 × 10-3
41) The average rate of disappearance of A between 20 s and 40 s is __________ mol/s.
A) 8.5 × 10-4
B) 1.7 × 10-3
C) 590
D) 7.1 × 10-3
E) 1.4 × 10-3
42) The average rate of appearance of B between 20 s and 30 s is __________ mol/s.
A) +1.5 × 10-3
B) +5.0 × 10-4
C) -1.5 × 10-3
D) +7.3 × 10-3
E) -7.3 × 10-3
43) How many moles of B are present at 10 s?
A) 0.011
B) 0.220
C) 0.110
D) 0.014
E) 1.4 × 10-3
44) How many moles of B are present at 30 s?
A) 2.4 × 10-3
B) 0.15
C) 0.073
D) 1.7 × 10-3
E) 0.051
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Chemical Equilibrium
1) At equilibrium, __________.
A) all chemical reactions have ceased
B) the rates of the forward and reverse reactions are equal
C) the rate constants of the forward and reverse reactions are equal
D) the value of the equilibrium constant is 1
E) the limiting reagent has been consumed
2) Which one of the following will change the value of an equilibrium constant?
A) changing temperature
B) adding other substances that do not react with any of the species involved in the equilibrium
C) varying the initial concentrations of reactants
D) varying the initial concentrations of products
E) changing the volume of the reaction vessel
3) Which of the following expressions is the correct equilibrium-constant expression for the equilibrium
between dinitrogen tetroxide and nitrogen dioxide?
N2O4 (g)
A)
B)
C)
2NO2 (g)
 NO 2 
 N 2O4 
2
 NO 2 
 N 2O4 
 NO2 
2
 N 2O4 
D) [NO2][N2O4]
E) [NO2]2[N2O4]
4) Which of the following expressions is the correct equilibrium-constant expression for the following reaction?
CO2 (g) + 2H2 (g)
CH3OH (g)
 CH3OH 
CO 2 
CH3OH 
B)
CO2  H 2 
2
CO 2  H 2 

C)
CH3OH 
CO2  H 2 
D)
CH3OH 
A)
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E)
CH3OH 
2
CO2  H 2 
5) The equilibrium-constant expression depends on the __________ of the reaction.
A) stoichiometry
B) mechanism
C) stoichiometry and mechanism
D) the quantities of reactants and products initially present
E) temperature
6) The value of Keq for the following reaction is 0.25:
SO2 (g) + NO2 (g)
SO3 (g) + NO (g)
The value of Keq at the same temperature for the reaction below is __________.
2SO2 (g) + 2NO2 (g)
2SO3 (g) + 2NO (g)
A) 0.50
B) 0.063
C) 0.12
D) 0.25
E) 16
7) The Keq for the equilibrium below is 7.52 × 10-2 at 480.0°C.
2Cl2 (g) + 2H2O (g)
4HCl (g) + O2 (g)
What is the value of Keq at this temperature for the following reaction?
4HCl (g) + O2 (g)
2Cl2 (g) + 2H2O (g)
A) 0.0752
B) -0.0752
C) 13.3
D) 5.66 × 10-3
E) 0.150
8) The Keq for the equilibrium below is 5.4 × 1013 at 480.0°C.
2NO (g) + O2 (g)
2NO2 (g)
What is the value of Keq at this temperature for the following reaction?
4NO (g) + 2O2 (g)
4NO2 (g)
A) 5.4 × 1013
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B) 5.4 × 10-13
C) 1.9 × 1012
D) 1.9 × 10-12
E) 2.9 × 1027
9) The Keq for the equilibrium below is 7.52 × 10-2 at 480.0°C.
2Cl2 (g) + 2H2O (g)
4HCl (g) + O2 (g)
What is the value of Keq at this temperature for the following reaction?
2HCl (g) +
1
O2 (g)
2
Cl2 (g) + H2O (g)
A) 13.3
B) 3.65
C) -0.0376
D) 5.66 × 10-3
E) 0.274
10) The Keq for the equilibrium below is 5.4 × 1013 at 480.0°C.
2NO (g) + O2 (g)
2NO2 (g)
What is the value of Keq at this temperature for the following reaction?
NO2 (g)
NO (g) + 1/2 O2 (g)
A) 5.4 × 10-13
B) 5.4 × 1013
C) 1.4 × 10-7
D) 5.66 × 10-3
E) none of the above
11) The Keq for the equilibrium below is 0.112 at 700.0°C.
1
O2 (g)
SO3 (g)
2
What is the value of Keq at this temperature for the following reaction?
SO2 (g) +
SO3 (g)
SO2 (g) +
1
O2 (g)
2
A) 0.224
B) 0.0125
C) 0.112
D) 8.93
E) -0.112
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12) Which of the following expressions is the correct equilibrium-constant expression for the reaction below?
2SO2 (g) + O2 (g)
2SO3 (g)
A) [SO3] / [SO2][O2]
B) [SO2] / [SO3]
C) [SO3]2 / [SO2]2[O2]
D) [SO3]2 / [SO2]2[O2]2
E) [SO3] / [SO2][O2]2
13) Which of the following expressions is the correct equilibrium-constant expression for the reaction below?
(NH4)2Se (s)
2NH3 (g) + H2Se (g)
A) [NH3][H2Se] / [(NH4)2Se]
B) [(NH4)2Se] / [NH3]2[H2Se]
C) 1 / [(NH4)2Se]
D) [NH3]2[H2Se]
E) [NH3]2[H2Se] / [(NH4)2Se]
14) Which of the following expressions is the correct equilibrium-constant expression for the reaction below?
H+ (aq) + HCO3- (aq)
CO2 (s) + H2O (l)
A) [H+][HCO3-] / [CO2]
B) [CO2] / [H+][HCO3-]
C) [H+][HCO3-] / [CO2][H2O]
D) [CO2][H2O] / [H+][HCO3-]
E) [H+][HCO3-]
15) The equilibrium constant for the gas phase reaction
N2 (g) + 3H2 (g)
2NH3 (g)
is Keq = 4.34 × 10-3 at 300°C. At equilibrium, __________.
A) products predominate
B) reactants predominate
C) roughly equal amounts of products and reactants are present
D) only products are present
E) only reactants are present
16) The equilibrium constant for the gas phase reaction
2SO2 (g) + O2 (g)
2SO3 (g)
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is Keq = 2.80 × 102 at 999 K. At equilibrium, __________.
A) products predominate
B) reactants predominate
C) roughly equal amounts of products and reactants are present
D) only products are present
E) only reactants are present
17) The equilibrium constant for the gas phase reaction
2NH3 (g)
N2 (g) + 3H2 (g)
is Keq = 230 at 300°C. At equilibrium, __________.
A) products predominate
B) reactants predominate
C) roughly equal amounts of products and reactants are present
D) only products are present
E) only reactants are present
18) Of the following equilibria, only __________ will shift to the right in response to a decrease in volume.
A) H2 (g) + Cl2 (g)
2 HCl (g)
B) 2 SO3 (g)
2 SO2 (g) + O2 (g)
C) N2 (g) + 3 H2 (g)
2 NH3 (g)
D) 2 Fe2O3 (s)
4 Fe (s) + 3 O2 (g)
E) 2HI (g)
H2 (g) + I2 (g)
19) The reaction below is exothermic:
2SO2 (g) + O2 (g)
2SO3 (g)
Le Châtelier's Principle predicts that __________ will result in an increase in the number of moles of SO3 (g) in
the reaction container.
A) increasing the pressure
B) decreasing the pressure
C) increasing the temperature
D) removing some oxygen
E) increasing the volume of the container
20) For the endothermic reaction
CaCO3 (s)
CaO (s) + CO2 (g)
Le Châtelier's principle predicts that __________ will result in an increase in the number of moles of CO2.
A) increasing the temperature
B) decreasing the temperature
C) increasing the pressure
D) removing some of the CaCO3 (s)
E) none of the above
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21) Consider the following reaction at equilibrium:
2SO2 (g) + O2 (g)
2SO3 (g) ΔH° = -99 kJ
Le Châtelier's principle predicts that an increase in temperature will result in __________.
A) a decrease in the partial pressure of SO3
B) a decrease in the partial pressure of SO2
C) an increase in Keq
D) no changes in equilibrium partial pressures
E) the partial pressure of O2 will decrease
22) The effect of a catalyst on an equilibrium is to __________.
A) increase the rate of the forward reaction only
B) increase the equilibrium constant so that products are favored
C) slow the reverse reaction only
D) increase the rate at which equilibrium is achieved without changing the composition of the equilibrium
mixture
E) shift the equilibrium to the right
23) The Keq for the equilibrium below is 7.73 × 10-2 at 500.0°C.
2Cl2 (g) + 2H2O (g)
4HCl (g) + O2 (g)
What is the value of Keq at this temperature for the following reaction?
1
Cl2 (g) + H2O (g)
2HCl (g) +
O2 (g)
2
A) 0.0773
B) 5.98 × 10-3
C) 0.278
D) 0.0376
E) 0.150
24) At 1000.0 K, the equilibrium constant for the reaction
2NO (g) + Br2 (g)
2NOBr (g)
is Kp = 0.017. Calculate Kp for the reverse reaction,
2NOBr (g)
A) 0.017
B) 1.6 × 10-4
C) 59
D) 0.99
E) 1.1
2NO (g) + Br2 (g).
25) At elevated temperatures, molecular hydrogen and molecular bromine react to partially form hydrogen
bromide:
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H2 (g) + Br2 (g)
2HBr (g)
A mixture of 0.682 mol of H2 and 0.440 mol of Br2 is combined in a reaction vessel with a volume of 2.00 L.
At equilibrium at 700 K, there are 0.556 mol of H2 present. At equilibrium, there are __________ mol of Br2
present in the reaction vessel.
A) 0.000
B) 0.440
C) 0.556
D) 0.126
E) 0.314
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