converted to B molecules (shaded spheres). Given the following pictures at t = 0 seconds and t =
100 seconds, which picture represents the number of A and B molecules remaining at 200
seconds?
A) picture a)
B) picture b)
C) picture c)
D) picture d)
122) Consider the first-order decomposition of A molecules (shaded spheres) in two vessels of
equal volume. What is the half-life of decomposition in vessel (b) relative to the half-life of
decomposition in vessel (a)?
A) half-life in vessel (b)/half-life in vessel (a) = 4:1
B) half-life in vessel (b)/half-life in vessel (a) = 2:1
C) half-life in vessel (b)/half-life in vessel (a) = 3:2
D) half-life in vessel (b)/half-life in vessel (a) = 1:1
123) Consider the first-order decomposition of A molecules (shaded spheres) in two vessels of
equal volume. What is the half-life of decomposition in vessel (b) relative to the half-life of
decomposition in vessel (a)?
A) half-life in vessel (b)/half-life in vessel (a) = 4:1
B) half-life in vessel (b)/half-life in vessel (a) = 2:1
C) half-life in vessel (b)/half-life in vessel (a) = 3:2
D) half-life in vessel (b)/half-life in vessel (a) = 1:1
124) Consider the first-order decomposition of A molecules (shaded spheres) in two vessels of
equal volume. How will the rate of decomposition in vessel (a) be affected if the volume of the
vessel is decreased by a factor of 2?
A) decrease by 1/2
B) increase by 2
C) increase by 4
D) stay the same
125) Consider the first-order decomposition of A molecules (shaded spheres) in two vessels of
equal volume. How will the half-life of decomposition in vessel (a) be affected if the volume of
the vessel is decreased by a factor of 2?
A) decrease by 1/2
B) increase by 2
C) increase by 4
D) stay the same
Consider the first-order reaction A → B in which A molecules (shaded spheres) are converted to
B molecules (unshaded spheres).
126) Which drawing (a)-(d) represents the reaction mixture at t = 2 minutes?
A) drawing (a)
B) drawing (b)
C) drawing (c)
D) drawing (d)
127) Which drawing (a)-(d) represents the reaction mixture at t = 3 minutes?
A) drawing (a)
B) drawing (b)
C) drawing (c)
D) drawing (d)
The following pictures represent the progress of a reaction in which two A molecules combine to
give a more complex molecule A2, 2A → A2.
128) What is the order of reaction with respect to A?
A) 0
B) 1/2
C) 1
D) 2
129) What is the time required to achieve the molecular mixture in drawing (d)?
A) 4 min
B) 5 min
C) 7 min
D) 8 min
45
130) Which of the elementary reactions shown above has a molecularity of one?
A) elementary reaction (a)
B) elementary reaction (b)
C) elementary reaction (c)
D) elementary reactions (a), (b), and (c)
131) Which of the elementary reactions shown above has a molecularity of two?
A) elementary reaction (a)
B) elementary reaction (b)
C) elementary reaction (c)
D) elementary reactions (a), (b), and (c)
132) Which of the elementary reactions shown above has a molecularity of three?
A) elementary reaction (a)
B) elementary reaction (b)
C) elementary reaction (c)
D) elementary reactions (a), (b), and (c)
Consider a reaction that occurs by the following one-step mechanism:
A2 + B2 → 2 AB
The potential energy profile for this reaction is shown below.
133) What is the species present at reaction stage 1?
A) an intermediate
B) a product
C) a reactant
D) a transition state
134) What is the species present at reaction stage 2?
A) an intermediate
B) a product
C) a reactant
D) a transition state
135) What is the species present at reaction stage 3?
A) an intermediate
B) a product
C) a reactant
D) a transition state
136) The activation energy for the forward reaction is given by the difference in energy between
which two reaction stages?
A) reaction stage 2 — reaction stage 1
B) reaction stage 2 — reaction stage 3
C) reaction stage 1 — reaction stage 3
D) reaction stage 3 — reaction stage 1
137) The energy of reaction, ΔE, is given by the difference in energy between which two
reaction stages?
A) reaction stage 2 — reaction stage 1
B) reaction stage 2 — reaction stage 3
C) reaction stage 1 — reaction stage 3
D) reaction stage 3 — reaction stage 1
Consider a reaction that occurs by the following mechanism:
A + BC → AC + B
AC + D → A + CD
The potential energy profile for this reaction is shown below.
138) Transition states occur at which reaction stages?
A) reaction stages 1 and 5
B) reaction stages 2, 3, and 4
C) reaction stages 2 and 4
D) reaction stage 3
139) Intermediates occur at which reaction stages?
A) reaction stages 1 and 5
B) reaction stages 2, 3, and 4
C) reaction stages 2 and 4
D) reaction stage 3
140) What is the activation energy for the formation of ozone?
A) 14 kJ
B) 392 kJ
C) 406 kJ
D) none of these
141) What is the activation energy for the destruction of ozone?
A) 14 kJ
B) 392 kJ
C) 406 kJ
D) none of these
12.2 Algorithmic Questions
1) The reaction that occurs in a Breathalyzer, a device used to determine the alcohol level in a
person’s bloodstream, is given below. If the rate of appearance of Cr2(SO4)3 is 1.64 mol/min at
a particular moment, what is the rate of disappearance of C2H6O at that moment?
2 K2Cr2O7 + 8 H2SO4 + 3 C2H6O → 2 Cr2(SO4)3 + 2 K2SO4 + 11 H2O
A) 0.547 mol/min
B) 1.09 mol/min
C) 2.46 mol/min
D) 4.92 mol/min
2) The decomposition of dinitrogen pentoxide is described by the chemical equation
2 N2O5(g) → 4 NO2(g) + O2(g)
If the rate of disappearance of N2O5 is equal to 1.60 mol/min at a particular moment, what is the
rate of appearance of NO2 at that moment?
A) 0.800 mol/min
B) 1.60 mol/min
C) 3.20 mol/min
D) 6.40 mol/min
3) The decomposition of dinitrogen pentoxide is described by the chemical equation
2 N2O5(g) → 4 NO2(g) + O2(g)
If the rate of appearance of NO2 is equal to 0.560 mol/min at a particular moment, what is the
rate of appearance of O2 at that moment?
A) 0.140 mol/min
B) 0.280 mol/min
C) 1.12 mol/min
D) 2.24 mol/min
4) The decomposition of dinitrogen pentoxide is described by the chemical equation
2 N2O5(g) → 4 NO2(g) + O2(g)
If the rate of appearance of O2 is equal to 3.00 mol/min at a particular moment, what is the rate
of disappearance of N2O5 at that moment?
A) 0.750 mol/min
B) 1.50 mol/min
C) 6.00 mol/min
D) 12.0 mol/min
5) For a reaction that follows the general rate law, Rate = k[A][B]2, what will happen to the rate
of reaction if the concentration of A is increased by a factor of 5.00? The rate will
A) decrease by a factor of 1/25.0.
B) decrease by a factor of 1/5.00.
C) increase by a factor of 5.00.
D) increase by a factor of 25.0.
6) For a reaction that follows the general rate law, Rate = k[A][B]2, what will happen to the rate
of reaction if the concentration of B is increased by a factor of 3.00? The rate will
A) decrease by a factor of 1/9.00.
B) decrease by a factor of 1/3.00.
C) increase by a factor of 3.00.
D) increase by a factor of 9.00.
7) What is the overall reaction order for the reaction that has the rate law: Rate = k[O2] [NO ]2?
A) zero order
B) first order
C) second order
D) third order
52
8) For a particular first-order reaction, it takes 24 minutes for the concentration of the reactant to
decrease to 25% of its initial value. What is the value for rate constant (in s-1) for the reaction?
A) 2.0 × 10-4 s-1
B) 9.6 × 10-4 s-1
C) 1.2 × 10-2 s-1
D) 5.8 × 10-2 s-1
9) The first-order reaction, SO2Cl2 → SO2 + Cl2, has a rate constant equal to 2.20 × 10-5 s-1 at
593 K. What percentage of the initial amount SO2Cl2 will remain after 6.00 hours?
A) 1.00%
B) 37.8%
C) 40.2%
D) 62.2%
10) The first-order reaction, 2 N2O(g) → 2 N2(g) + O2(g), has a rate constant equal to 0.76 s-1
at 1000 K. How long will it take for the concentration of N2O to decrease to 12% of its initial
concentration?
A) 0.62 s
B) 2.8 s
C) 6.3 s
D) 8.4 s
11) The isomerization reaction, CH3NC → CH3CN, is first order and the rate constant is equal
to 0.46 s-1 at 600 K. What is the concentration of CH3NC after 0.20 minutes if the initial
concentration is 0.30 M?
A) 1.2 × 10-3 M
B) 2.7 × 10-3 M
C) 1.2 × 10-1 M
D) 2.7 × 10-1 M
12) The following reaction is first order, C2H6 → 2 CH3. If the rate constant is equal to 5.5 ×
10-4 s-1 at 1000 K, how long will it take for 0.35 mol of C2H6 in a 1.00 L container to decrease
to 0.20 mol in the same container?
A) 4.5 min
B) 17 min
C) 53 min
D) 65 min
13) The rate constant, k, for a first-order reaction is equal to 4.2 × 10-4 s-1. What is the half-life
for the reaction?
A) 2.9 × 10-4 s
B) 1.2 × 103 s
C) 1.7 × 103 s
D) 2.4 × 103 s
14) The first-order reaction, SO2Cl2 → SO2 + Cl2, has a half-life of 8.75 hours at 593 K. How
long will it take for the concentration of SO2Cl2 to fall to 16.5% of its initial value?
A) 0.143 hr
B) 2.28 hr
C) 6.99 hr
D) 22.7 hr
15) For the first-order reaction, 2 N2O(g) → 2 N2(g) + O2(g), what is the concentration of N2O
after 3 half-lives if mol of N2O is initially placed into a 1.00-L reaction vessel?
A) 1.6 × 10-2 M
B) 3.1 × 10-2 M
C) 6.2 × 10-2 M
D) 1.2 × 10-1 M
16) Carbon-14, which is present in all living tissue, radioactively decays via a first-order process.
A one-gram sample of wood taken from a living tree gives a rate for carbon-14 decay of 13.6
counts per minute. If the half-life for carbon-14 is 5715 years, how old is a wood sample that
gives a rate for carbon-14 decay of 11.9 counts per minute?
A) 5.3 × 102 yr
B) 7.6 × 102 yr
C) 1.1 × 103 yr
D) 9.4 × 103 yr
17) In aqueous solution, hypobromite ion, BrO–, reacts to produce bromate ion, BrO3–, and
bromide ion, Br–, according to the following chemical equation.
A plot of 1/[BrO–] vs. time is linear and the slope is equal to 0.056 M-1s-1. If the initial
concentration of BrO– is 0.80 M, how long will it take one-half of the BrO– ion to react?
A) 4.5 × 10-2 s
B) 7.1 s
C) 12 s
D) 22 s
18) The second-order reaction 2 Mn(CO)5 → Mn2(CO)10, has a rate constant equal to 3.0 × 109
M-1 s-1 at 25°C. If the initial concentration of Mn(CO)5 is 2.0 × 10-5 M, how long will it take
for 90.% of the reactant to disappear?
A) 6.7 × 10-16 s
B) 7.4 × 10-15 s
C) 1.5 × 10-4 s
D) 6.0 × 103 s
19) Nitrogen dioxide decomposes at 300°C via a second-order process to produce nitrogen
monoxide and oxygen according to the following chemical equation.
2 NO2(g) → 2 NO(g) + O2(g).
A sample of NO2(g) is initially placed in a 2.50-L reaction vessel at 300°C. If the half-life and
the rate constant at 300°C are 11 seconds and 0.54 M-1 s-1, respectively, how many moles of
NO2 were in the original sample?
A) 0.17 mol
B) 0.42 mol
C) 5.9 mol
D) 15 mol
20) Hydrogen iodide decomposes at 800 K via a second-order process to produce hydrogen and
iodine according to the following chemical equation.
2HI(g) → H2(g) + I2(g)
At 800 K it takes 142 seconds for the initial concentration of HI to decrease from 6.75 × 10-2 M
to 3.50 × 10-2 M. What is the rate constant for the reaction at this temperature?
A) 5.12 × 10-4 M-1s-1
B) 9.69 × 10-2 M-1s-1
C) 10.3 M-1s-1
D) 1.95 × 103 M-1s-1
21) The activation for the following reaction is 180 kJ/mol:
(g) + (g) → (g)
If the rate constant at 202°C is 4.13 × 1 , what is the rate constant at 277°C?
A) 2.10 × 1
B) 1.66 × 1
C) 5.39×
D) 3.99 ×
22) The aquation of tris(1,10-phenanthroline)iron(II) in acid solution takes place according to the
equation:
Fe(phen)32+ + 3 H3O+ + 3 H2O → Fe(H2O)62+ + 3 phenH+.
If the activation energy, Ea, is 126 kJ/mol and the rate constant at 30°C is 9.8 × 10-3 min-1, what
is the rate constant at 35°C?
A) 4.4 × 10-3 min-1
B) 2.2 × 10-2 min-1
C) 4.5 × 101 min-1
D) 2.3 × 102 min-1
12.3 Short Answer Questions
1) For the reaction shown below, if the rate of formation of O2 is 6.0 × 10–6 M/s, the rate of
decomposition of N2O5 over the same time interval is ________.
2 N2O5(g) → 4 NO2(g) + O2(g)
2) The reaction shown below has the rate law: Rate = k[BrO3–][Br–][H+]2. The order of
reaction with respect to H+ is ________ and the overall order is ________.
BrO3–(aq) + 5 Br–(aq) + 6 H+(aq) → 3 Br2(aq) + 3 H2O(l)
3) At 300°C decomposition of NO2(g) occurs with a rate law: Rate = – k[NO2]x. If the initial
rate of decomposition is 3.2 × 10–5 M/s when [NO2]o = 8.0 × 10–3 M and the initial rate of
decomposition is 8.0 × 10–6 M/s when [NO2]o = 4.0 × 10–3 M, then the order of reaction with
respect to NO2, x = ________.
4) The decomposition of hydrogen peroxide occurs according to the equation
2 H2O2(aq) → 2 H2O(l) + O2(g)
A concentration-time study of this reaction produces a straight line when ln[H2O2] is plotted
versus time. Therefore, this is a ________ order reaction.
5) At 55° the decomposition of N2O5 is first order, having a rate constant, k = 1.7 × 10–3 s–1. If
the initial concentration of N2O5 is 6.4 × 10–3 M, the number of half-lives that are required for
the N2O5 concentration to fall to 2.0 × 10–4 M is ________, and the amount of time required is
________ minutes.
6) Carbon-14 has a half-life of 5715 years. Currently living organisms decay at a rate of 15.3
disintegrations/ min per gram of carbon. If an archeological artifact has a carbon-14 decay rate
of 12.0 disintegrations/ min per gram of carbon, the approximate age of the artifact is ________
years old.
7) At an elevated temperature the decomposition of a gaseous oxide, AO2 occurs with a rate
constant, k = 0.54 M–1s–1. If the half-life of this reaction is 926 seconds when [AO2] = 2.0 ×
10–3 M and 462 seconds when [AO2] = 4.0 × 10–3 M, this reaction is ________ order.
8) A gaseous compound, C, undergoes catalytic decomposition at an initial rate of 0.45 M/s
when [C]o = 3.0 × 10–3 M and 0.45 M/s when [C]o = 9.0 × 10–3 M. Therefore, this is a
________ order reaction.
9) A reaction occurs by a two-step mechanism, shown below.
Step 1: AX2(g) → AX(g) + X(g)
Step 2: AX2(g) + X(g) → AX + X2(g)
The intermediate in this reaction is ________, and the molecularity of the second step is
________.
10) A gaseous reaction occurs by a two-step mechanism, shown below.
Step 1: AX +Y2 → AXY2
Step 2: AXY2 + AX → 2 AXY
If the rate law for this reaction is Rate = k[AX]2[Y2], the intermediate is ________, and step
________ is the rate-determining step.
11) An aqueous reaction occurs by a two-step mechanism, shown below.
Step 1: A2X2 + Y → A2X + XY
Step 2: A2X2 + XY → A2X + X2 + Y
In this reaction the intermediate is ________, and the catalyst is ________.