Problem Set 13 - Department of Chemistry at Illinois State University

Chemistry 360
Spring 2015
Dr. Jean M. Standard
April 22, 2015
Problem Set 13
Good review problems in Engel & Reid (3rd Ed.): 35.31, 35.32, 35.35, 35.36, 35.37, 35.40
1.
"→ P follows second-order kinetics. The rate constant for the reaction is k=3.50×10–4
The reaction 2A "
Lmol–1s–1. Determine the time required for the concentration of A to drop from its initial value of 0.260 mol/L
to 0.011 mol/L.
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2.
One of the hazards of nuclear explosions is the generation of 90Sr and its subsequent incorporation into the
bones in place of calcium. Suppose 1 mg of 90Sr was absorbed into the body. How much will remain after 10
years, 20 years, and 50 years if none was lost metabolically? Note that 90Sr has a half-life of 28.1 years and that
nuclear decay follows first-order kinetics.
3.
"→ P follows second-order kinetics. Initially, the concentration of A was 0.075 mol/L.
The reaction 2A "
After 1 hour, the concentration had fallen to 0.020 mol/L. Determine the rate constant for the reaction and the
half-life.
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4.
k
k
–1
1 → B ""
2→ C
A particular consecutive reaction, A ""
, has rate constants given by k1 = 0.01s and
k 2 = 0.001s –1 . Sketch a graph of [A], [B], and [C] as functions of time and calculate the time at which the
intermediate B reaches its maximum concentration.
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5.
The gas phase decomposition of acetic acid at high temperature (1189 K) proceeds by way of two parallel
reactions,
k
CH 3COOH
1→
""
CH 3COOH
2
""
→
k
CH 4 + CO 2
k1 = 3.74 s –1
H 2C = C = O + H 2O
k 2 = 4.65 s –1.
Calculate the ratio of ketene (H2C=C=O) concentration to methane concentration and determine the maximum
percent yield
€ of ketene (H2C=C=O).
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6.
For the reaction A + B
C + D , various initial rate measurements were made starting with A and
B only and then C and D only. From the data below, calculate the equilibrium constant for the reaction.
[A]o
[B]o
Initial Rate
(mol/L)
(mol/L)
(molL–1s–1)
0.660
1.23
1.081×10–5
4.01
1.23
6.577×10–5
4.01
2.25
6.568×10–5
[C]o
[D]o
Initial Rate
(mol/L)
(mol/L)
(molL–1s–1)
2.88
0.995
7.805×10–7
2.88
1.65
1.290×10–6
1.01
1.65
1.300×10–6
7.
The second-order rate constant for the decomposition of a certain substance is 1.70×10–2 Lmol–1s–1 at 30ºC and
2.01×10–2 Lmol–1s–1 at 37ºC. Determine the activation energy and pre-exponential factor.
8.
Nitrous oxide, N2O, decomposes thermally at high temperatures. The measured rate constants for the gas phase
decomposition of N2O at different temperatures [S. K. Ross et al., J. Phys. Chem. A 1997, 101, 1104] are given
in the table below.
T (K)
k (cm3 molecule–1 s–1)
2056
6.79×10–16
2095
8.38×10–16
2132
1.03×10–15
2173
1.39×10–15
Assuming Arrhenius behavior, determine the activation energy (in kJ/mol) and the pre-exponential factor (in
units of cm3 molecule–1 s–1).
9.
Many reactions double their rates with a 10˚C rise in temperature. Assume that the rate of a reaction is
measured at 305 and 315 K. What must the energy of activation be if the rate of reaction at 315 K is twice the
rate of reaction at 305 K?