Welcome to Chem 1A CLAS with Eric Engel

Kinetics (Ch 15)
1. For the reaction: A + 3B  2C
a. If at some point the rate of production of C is 0.24 M/s, what is
the rate of change of B?
b. The following data was collected for this reaction at 25 ˚C.
What is the differential rate law?
Expt
1
2
3
[A]0
0.10
0.10
0.20
[B]0
0.10
0.20
0.10
c. What is the overall order of the reaction?
d. What is the rate constant?
Initial rate (M/s)
1.2 x 10-4
4.8 x 10-4
2.4 x 10-4
Kinetics (Ch 15)
2. Given the following data for the reaction:
2A + B + C D + 3E
Determine the differential rate law.
Expt
[A]0
[B]0
[C]0
Initial rate (mol/L s)
1
0.020
0.010
0.020
0.0050
2
0.040
0.010
0.020
0.0100
3
0.020
0.010
0.060
0.0050
4
0.040
0.040
0.020
0.160
Kinetics (Ch 15)
Kinetics (Ch 15)
3. The decomposition of nitrogen dioxide,
2 NO2 2NO + O2,
obeys the rate law rate = k[NO2]2. For this
reaction the rate constant, k = 1.8 x 10-2 L/mol s
at 500 K. If the initial concentration of NO2 is
1.2 M, how long will it take for the concentration
to decrease by 25%?
Kinetics (Ch 15)
4. The thermal decomposition of phosphine, PH3,
into phosphorous and hydrogen is a first order
reaction. The half-life for this reaction is 35 sec
at 680 ˚C.
a. Calculate the time required for 95% of the
phosphine to decompose.
b. What fraction of phosphine remains after 70 sec?
Kinetics (Ch 15)
5. The successive half-lives for a certain reaction
were measured to be 10, 20 and 40 minutes. If
the initial concentration of the reactant was
1.0 M, how much was left after 80 min of
reaction time?
Kinetics (Ch 15)
6. Given the following mechanism:
H2O2  H2O + O
O + CF2Cl2  ClO + CF2Cl
ClO + O3  Cl + 2O2
Cl + CF2Cl  CF2Cl2
a. Write the overall reaction.
b. Identify any intermediate(s).
c. Identify any catalyst.
d. Write the rate law for each step.
Kinetics (Ch 15)
7. For the following reaction, the rate law was
determined to be r = k [NO]2 [O2]
2 NO + O2  2 NO2
Determine whether or not the following mechanisms are
consistent with this rate law.
a. NO + O2  NO2 + O slow
O + NO  NO2
fast
b. NO + O2  NO3
fast equilibrium
NO3 + NO  2NO2 slow
Kinetics (Ch 15)
8. The forward activation energy for a reaction is
60 kJ/mol. If ΔE for the reaction is 45 kJ/mol,
what is the activation energy for the reverse
reaction?
Kinetics (Ch 15)
9. What factors affect the rate constant for a
reaction?
Kinetics (Ch 15)
10. The rate constants for a certain second order
reaction are 3.20 x 10-2 1/M s at 24 ˚C and
9.45 x 10-1 1/M s at 150 ˚C.
a. Calculate the activation energy for the
reaction.
b. What is the rate constant at 100 ˚C?
Kinetics (Ch 15)
Bonus Q: How would the addition of a catalyst
change the energy values in #8?