Question

Select the most likely rate law for the following:
(CH3)3C-Br + OH- > (CH3)3C-OH + Br-

a. Rate=k[(CH3)3C-Br]
b. Rate=k[(CH3)3C-Br][OH-]
c. Rate=k[(CH3)3C-Br][OH-]2
d. Rate=k[(CH3)3C-Br]2[OH-]2
e. Rate=k[(CH3)3C-Br]2[OH-]

The correct is answer is "a" but I'm not sure why its not b. Can you help?

Answer 1

Well, if the concentration of OH- were near zero, the rate would b......

I agree b is the general answer.
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a+b=c

rate is =k[a][b]
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<b>However</b>, warning: if
a+b=c and b is in great concentration, and remains so during the reaction, then
rate= k'[a] where k' is a pseudo constant. I do not know in this reaction as you have listed it if -OH is in great concentration.

If for example you had KOH in solution, of a nice concentration, then the rate would be answer a).

So, "most likely" means OH- is in great concentration, and will remain constant, so choose answer a), the order 1 reaction.