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

1. H2O2(aq) + I-(aq) → H2O(l) + IO-(aq) (slow)
2. IO-(aq) + H2O2(aq) → H2O(l) + O2(g) + I-(aq) (fast)

a. Assuming that the first step of the mechanism is rate determining, predict the rate expression for the overall process. b. Write the chemical equation for the overall process. c. Identify the intermediate, if any, in the mechanism. d. What distinguishes an intermediate from a catalyst in a chemical reaction?

a. I was never very good at rate-determining steps. I'd have to brush up on this, sorry.

b. The overall reaction is just the sum of the two equations. Add the left sides, add the right sides, and delete anything that appears on both sides in equal molar amounts.

c. The intermediate is obviously the thing you deleted in #2.

d. An intermediate is a distinct chemical. The catalyst is regenerated from it. In some catalyzed reactions, the catalyst does not change (metal surfaces, for example).

The overall rate of the reaction is equal to the rate of the slowest step in the sequence which is the rate-determining step.
rate = k [H2O2][I]