## Chemical Kinetics

The following problems are taken from T. L. Brown, H. E. Lemay, B. E. Bursten, & J. R. Burdge, Chemistry: The Central Science, Ninth Edition, Chapter 14. To see the solution to a problem or to return from the solution, click on the number of the problem.

12)  (a) Consider the combustion of ethylene, C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(g). If the concentration of C2H4 is decreasing at the rate of 0.23 M/s, what are the rates of change in the concentration of CO2 and H2O?

(b) The rate of decrease in N2H4 partial pressure in a closed reaction vessel from the reaction, N2H4(g) + H2(g) 2NH3(g), is 45 torr/hr. What are the rates of change of NH3 partial pressure and total pressure in the vessel?

22) The reaction 2ClO2(aq) + 2OH-(aq) ClO3-(aq) + ClO2-(aq) + H2O(l) was studied with the following results:

Experiment          [ClO2], M          [OH-], M          Rate, M/s

1                       0.060                  0.030                0.0248
2                       0.020                  0.030                0.00276
3                       0.020                  0.090                0.00828

(a) Determine the rate law for the reaction.

(b) Calculate the rate constant.

(c) Calculate the rate when [ClO2] = 0.010 M and [OH-] = 0.015 M.

32) The first-order rate constant for the decomposition of N2O5, N2O5(g) 2NO2(g) + O2(g) at 70°C is 6.82 x 10-3s-1. Suppose we start with 0.0250 mol of N2O5(g) in a volume of 2.0 L.

(a) How many moles of  N2O5 will remain after 2.5 min?

(b) How many minutes will it take for the quantity of N2O5 to drop to 0.010 mol?

(c) What is the half-life of N2O5 at 70°C?

42) (a) The activation energy for the isomerization of methyl isonitrile is 160 kJ/mol. Calculate the fraction of methyl isonitrile molecules that have an energy of 160.0 kJ or greater at 500 K.

(b) Calculate this fraction for a temperature of 510 K. What is the ratio of the fraction at 510 K to that of 500 K?

60) The following mechanism has been proposed for the reaction of NO with H2 to form N2O and H2O:

NO(g) + NO(g) N2O2(g)

N2O2(g) + H2(g) N2O(g) + H2O(g)

(a) Show that the elementary steps of the proposed mechanism add to provide a balanced equation for the reaction.

(b) Write a rate law for each elementary step in the mechanism.

(c) Identify any intermediates in the mechansim.

(d) The observed rate law is rate = k[NO]2[H2]. If the proposed mechanism is correct, what can we conclude about the relative speeds of the first and second steps?

76) The reaction 2NO(g) + O2(g) 2NO2(g) is second order in NO and first order in O2. When [NO] = 0.040 M and [O2] = 0.035 M, the observed rate of disappearance of NO is 9.3 x 10-5 M/s.

(a) What is the rate of disappearance of O2 at this moment?

(b) What is the value of the rate constant?

(c) What are the units of the rate constant?

(d) What would happen to the rate if the concentration of NO were increased by a factor of 1.8?

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