The bromination of acetone is acid-catalyzed:
The rate of disappearance of bromine was measured for several different concentrations of acetone, bromine, and
|
|
|
Rate of Disappearance of
|
|
(1) |
0.30 |
0.050 |
0.050 |
|
(2) |
0.30 |
0.10 |
0.050 |
|
(3) |
0.30 |
0.050 |
0.10 |
|
(4) |
0.40 |
0.050 |
0.20 |
|
(5) |
0.40 |
0.050 |
0.050 |
|
(a) What is the rate law for the reaction? (b) Determine the rate constant. (c) The following mechanism has been proposed for the reaction:
Show that the rate law deduced from the mechanism is consistent with that shown in part (a).
Interpretation:
The rate law and rate constant for the reaction are to be determined. The rate law is consistent with the mechanism shown in part (a), is to be determined.
Concept introduction:
The rate of reaction in terms of concentration is called the rate law.
The step-by-step reaction is called the reaction mechanism. The reaction that takes place in a single step is called an elementary reaction.
Answer to Problem 85AP
Solution:
(a)
(b)
(c) The rate law deduced from the mechanism is consistent.
Explanation of Solution
a)The rate law for the reaction
For the determination of rate law, calculate the exponents as follows:
Based on
Based on
Based on
Based on
Hence, the rate law for the reaction is:
b)The rate constant
According to rate law, the rate constant for the reaction is:
Rearrange the above equation for
Here,
From experiment 1,
The rate law is
The concentration of
Substitute,
The rate constant for the reaction is
c) The rate law deduced from the given following mechanism is consistent or not with
The proposed mechanism for the reaction is:
Let the rate constant for the slow step be
…… (1)
The rate constants for the forward and reverse steps in the fast equilibrium are
…… (2)
So, equation (1) becomes
The overall equation from part (a) is:
From equation (3) and (4),
So, the rate law is consistent with the mechanism shown in part (a).
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Chapter 14 Solutions
Chemistry
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