Question

Consider the following mechanism for the oxidation of bromide ions by hydrogen peroxide in aqueous acid solution.

H+ + H2O2 ↔ H2O+-OH (rapid equilibrium)

H2O+-OH + Br-→ HOBr + H2O (slow)

HOBr + H+ + Br- → Br2 + H2O (fast)

Which of the following rate laws is consistent with the mechanism?


Select one:
a. Rate = k [H2O+-OH][Br-]
b. Rate = k[Br-]
c. Rate = k[HOBr][H+][Br-][H2O2]
d. Rate = k[H2O2][H+][Br-]
e. Rate = k[H2O2][H+]2[Br-]

Answer 1

Answer:

a. Rate = k [H2O+-OH][Br-]

Explanation:

For a reaction:

nA+xB→C+D

The rate of the reaction is:

Rate = [A]ⁿ[B]ˣ

Now, in a mechanism, the rate of the reaction depends of the slow step. In the problem:

H2O+-OH + Br-→ HOBr + H2O

And the rate is:

a. Rate = k [H2O+-OH][Br-]