A.P. Chemistry Chapter 14 Kinetics Problem Set

1.  Dinitrogen pentoxide (N2O5) decomposes in chloroform as a solvent to yield NO2 and O2. The decomposition is first order with a rate constant at 450C of 1.0 x 10-5 s-1. Calculate the partial pressure of O2 produced from 1.00 L of 0.600 M N2O5 solution at 450C over a period of 20.0 hr if the gas is collected in a 10.0-L container. (Assume that the products do not dissolve in chloroform)

2.  Zinc metal dissolves in hydrochloric acid according to the reaction:

Zn(s) + 2 HCl(aq) è ZnCl2(aq) + H2(g)

Suppose you are asked to study the kinetics of this reaction by monitoring the rate of production of H2(g).

a)  By using a reaction flask, a manometer, and any other common laboratory equipment, design an experimental apparatus that would allow you to monitor the partial pressure of H2(g) produced as a function of time.

b)  Explain how you would use the apparatus to determine the rate law of the reaction.

c)  Explain how you would use the apparatus to determine the reaction order of [H+] for the reaction.

d)  How could you use the apparatus to determine the activation energy of the reaction?

e)  Explain how you would use the apparatus to determine the effects of changing the form of the Zn(s) from metal strips to granules.

3.  Enzymes, the catalysts of biological systems, are high molecular weight protein materials. The active site of the enzyme is formed by the 3-D arrangement of the protein in solution. When heated, proteins undergo denaturation, a process in which the 3-D structure of the protein unravels, at least partly. The graph shows the variation of enzyme activity with temperature.

  1. What role does denaturation play in the shape of the curve?
  2. How does the answer to (a) fit in with the lock-and-key model of enzyme action?
  3. At what approximate temperature would this enzyme be most active?
  4. Would this enzyme be commonly found in the human body? If so, where?

4.  The following mechanism has been proposed for the gas-phase reaction of chloroform (CHCl3) and chlorine:

Step 1: Cl2(g) ó 2 Cl(g) (fast)

Step 2: Cl(g) + CHCl3(g) è HCl(g) + CCl3(g) (slow)

Step 3: Cl(g) + CCl3(g) è CCl4 (fast)

a)  What is the overall reaction?

b)  What are the intermediates in the mechanism?

c)  What is the molecularity of each of the elementary reactions?

d)  What is the rate-determining step?

e)  What is the rate law predicted by this mechanism? (Hint: The overall reaction order is not an integer.)