1. What Is Meant by the Rate Determining Step? (1)

Name:______Date:______Period:_____

WS Rxn Mechanisms

1.  What is meant by the rate determining step? (1)

2.  Consider the following reaction:

A + B → C

the mechanism is as follows:

A → D slow

D + B → R fast

R → C fast

What is the rate equation? (2)

Circle the rate determining step. (1)

What are the intermediates? (2)

3.  Why should you never include an intermediate in the rate law for an overall reaction? (1)

4.  Under what circumstances might you include a catalyst in the rate law for an overall reaction? (1)

5.  14.65. The following mechanism has been proposed for the gas-phase reaction of H2 with ICl:

(a) Write the balanced equation for the overall reaction. (1)

(b) Identify any intermediates in the mechanism. (1)

(c) If the first step is slow and the second one is fast, what rate law do you expect to be

observed for the overall reaction? (2)

6. 14.66. The decomposition of hydrogen peroxide is catalyzed by iodide ion. The catalyzed reaction is thought to proceed by a two-step mechanism:

(a) Write the chemical equation for the overall process. (2)

(b) Identify the intermediate, if any, in the mechanism. (1)

(c) Identify the catalyst, if any, in the mechanism. (1)

(d) Identify the rate determining step of the mechanism, and write the rate law

for the overall reaction. (2)

7. 14.68. You have studied the gas-phase oxidation of HBr by O2:

You find the reaction to be first order with respect to HBr and first order with respect to O2. You propose the following mechanism:

(a) Indicate how the elementary reactions add to give the overall reaction. (1)

[Hint: You will need to multiply the coefficients of one of the equations by 2.]

(b) Based on the rate law, which step is rate determining?

Label each step as fast or slow. (1)

(c) What are the intermediates in this mechanism? (2)

(d) If you are unable to detect HOBr or HOOBr among the products, does this disprove

your mechanism? Explain. (1)

8. 14.67. The reaction 2 NO(g) + Cl2(g) 2 NOCl(g) is found to follow the rate law, rate = k[NO]2[Cl2]. The following mechanism has been proposed for this reaction:

(a) What would the rate law be if the first step were rate determining? (1)

(b) Based on the observed experimental rate law, what can be concluded about the

relative rates of the two steps? (2)

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