Chemistry: The Central Science, 13e (Brown et al.)
Chapter 14 Chemical Kinetics
14.1 Multiple-Choice Questions
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) Which one of the following is not a valid expression for the rate of the reaction below?
4NH3 + 7O2 → 4NO2 + 6H2O
A) –
B)
C)
D) –
E) All of the above are valid expressions of the reaction rate.
4) 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
5) The rate law for this reaction is rate = ________.
A) k[A][B]
B) k[P]
C) k[A]2[B]
D) k[A]2[B]2
E) k[A]2
6) The magnitude of the rate constant is ________.
A) 38.0
B) 0.278
C) 13.2
D) 42.0
E) 2.21
The data in the table below were obtained for the reaction:
2 ClO2 (aq) + 2 OH– (aq) → ClO3– (aq) + ClO2– (aq) + H2O (1)
7) What is the order of the reaction with respect to ClO2?
A) 1
B) 0
C) 2
D) 3
E) 4
8) What is the order of the reaction with respect to OH–?
A) 0
B) 1
C) 2
D) 3
E) 4
9) What is the overall order of the reaction?
A) 4
B) 0
C) 1
D) 2
E) 3
10) What is the magnitude of the rate constant for the reaction?
A) 1.15 × 104
B) 4.6
C) 230
D) 115
E) 713
11) 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.
12) 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
B) 0.65
C) 0.81
D) 1.2
E) 0.54
13) The reaction
CH3–N≡C → CH3–C≡N
is a first-order reaction. At 230.3 °C, k = 6.29 × 10-4s-1. If is 1.00 × 10–3 initially,
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
14) 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)
15) 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.
16) The rate constant for this reaction is ________ s-1.
A) 6.9 × 10-2
B) 3.0 × 10-2
C) 14
D) 0.46
E) 4.0 × 102
17) 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
18) 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) 0.198
E) 3.30 ×10-3
19) 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
20) 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.
21) 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
22) 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
B) k
C) k[N2O5]
D) k
E) 2k[N2O5]
23) 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
24) 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
25) Which energy difference in the energy profile below corresponds to the activation energy for the
forward reaction?
A) x
B) y
C) x + y
D) x – y
E) y – x
26) In the energy profile of a reaction, the species that exists at the maximum on the curve is called the
________.
A) product
B) activated complex
C) activation energy
D) enthalpy of reaction
E) atomic state
27) In the Arrhenius equation,
k = Ae-Ea/RT
________ is the frequency factor.
A) k
B) A
C) e
D) Ea
E) R
28) 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
29) In general, as activation energy increases, 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
30) At elevated temperatures, methylisonitrile (CH3NC) isomerizes to acetonitrile (CH3CN):
CH3NC (g) → CH3CN (g)
The dependence of the rate constant on temperature is studied and the graph below is prepared from the
results.
The energy of activation of this reaction is ________ kJ/mol.
A) 160
B) 1.6 × 105
C) 4.4 × 10–7
D) 4.4 × 10-4
E) 1.9 × 104
31) The mechanism for formation of the product X is:
A + B → C + D (slow)
B + D → X (fast)
The intermediate reactant in the reaction is ________.
A) A
B) B
C) C
D) D
E) X
32) For the elementary reaction
NO3 + CO → NO2 + CO2
the molecularity of the reaction is ________, and the rate law is
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]
33) A possible mechanism for the overall reaction
Br2 (g) + 2NO (g) → 2NOBr (g)
is
NO (g) + Br2 (g) NOBr2 (g) (fast)
NOBr2 (g) + NO (g) 2NOBr (slow)
The rate law for formation of NOBr based on this mechanism is rate = ________.
A) k1[NO]1/2
B) k1[Br2]1/2
C) (k2k1/k-1)[NO]2[Br2]
D) (k1/k-1)2[NO]2
E) (k2k1/k-1)[NO][Br2]2
34) Which of the following is true?
A) If we know that a reaction is an elementary reaction, then we know its rate law.
B) The rate-determining step of a reaction is the rate of the fastest elementary step of its mechanism.
C) Since intermediate compounds can be formed, the chemical equations for the elementary reactions in a
multistep mechanism do not always have to add to give the chemical equation of the overall process.
D) In a reaction mechanism, an intermediate is identical to an activated complex.
E) All of the above statements are true.
35) 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
14
36) The rate law of the overall reaction
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.
37) 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.
38) The primary source of the specificity of enzymes is ________.
A) their polarity, which matches that of their specific substrate
B) their delocalized electron cloud
C) their bonded transition metal, which is specific to the target substrate
D) their locations within the cell
E) their shape, which relates to the lock-and-key model
39) ________ are used in automotive catalytic converters.
A) Heterogeneous catalysts
B) Homogeneous catalysts
C) Enzymes
D) Noble gases
E) Nonmetal oxides
40) The enzyme nitrogenase converts ________ into ________.
A) ammonia, urea
B) CO and unburned hydrocarbons, H2O and CO2
C) nitrogen, ammonia
D) nitrogen oxides, N2 and O2
E) nitroglycerine, nitric acid, and glycerine
41) The active site of nitrogenase is a cofactor that contains two transition metals. These transition metals
are ________.
A) Cr and Mg
B) Mn and V
C) Os and Ir
D) Fe and Zn
E) Fe and Mo
42) Nitrogen fixation is a difficult process because ________.
A) there is so little nitrogen in the atmosphere
B) nitrogen exists in the atmosphere primarily as its oxides which are very unreactive
C) nitrogen is very unreactive, largely due to its triple bond
D) of the extreme toxicity of nitrogen
E) of the high polarity of nitrogen molecules preventing them from dissolving in biological fluids, such as
those inside cells
14.2 Bimodal Questions
1) 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
2) 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.
3) 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
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:
4) 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
5) 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
6) 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
7) The average rate disappearance of A between 20 s and 30 s is ________ mol/s.
A) 5.0 × 10-4
B) 1.6 × 10-2
C) 1.5 × 10–3
D) 670
E) 0.15
8) 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
9) 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
The peroxydisulfate ion (S2O82-) reacts with the iodide ion in aqueous solution via the reaction:
S2O82- (aq) + 3I– → 2SO4 (aq) + I3– (aq)
An aqueous solution containing 0.050 M of S2O82- ion and 0.072 M of I– is prepared, and the progress of the
reaction followed by measuring [I–]. The data obtained is given in the table below.
10) The average rate of disappearance of I– between 400.0 s and 800.0 s is ________ M/s.
A) 2.8 × 10-5
B) 1.4 × 10-5
C) 5.8 × 10–5
D) 3.6 × 104
E) 2.6 × 10-4
11) The average rate of disappearance of I– in the initial 400.0 s is ________ M/s.
A) 6.00
B) 3.8 × 10-5
C) 1.4 × 10–4
D) 2.7 × 104
E) 3.2 × 10-4
12) The average rate of disappearance of I– between 1200.0 s and 1600.0 s is ________ M/s.
A) 1.8 × 10-5
B) 1.2 × 10-5
C) 2.0 × 10–5
D) 5.0 × 104
E) 1.6 × 10-4
13) The concentration of S2O82- remaining at 400 s is ________ M.
A) +0.015
B) +0.035
C) -0.007
D) +0.045
E) +0.057
14) The concentration of S2O82- remaining at 800 s is ________ M.
A) 0.046
B) 0.076
C) 4.00 × 10-3
D) 0.015
E) 0.041
15) The concentration of S2O82- remaining at 1600 s is ________ M.
A) 0.036
B) 0.014
C) 0.043
D) 0.064
E) 0.029
16) At elevated temperatures, dinitrogen pentoxide decomposes to nitrogen dioxide and oxygen:
2N2O5(g) → 4NO2 (g) + O2 (g)
When the rate of formation of NO2 is 5.5 × 10–4 M/s, the rate of decomposition of N2O5 is ________ M/s.
A) 2.2 × 10-3
B) 1.4 × 10-4
C) 10.1 × 10-4
D) 2.8 × 10-4
E) 5.5 × 10-4