Rate laws for reactions are affected by the position of the rate-determining step in the overall reaction mechanism.

Slow Step Followed by a Fast Step

As discussed in the previous concept, if the first step in a reaction mechanism is the slow, rate-determining step, then the overall rate law for the reaction is easy to write, and simply follows the stoichiometry of the initial step. For example, consider the following reaction:

Fast Step Followed by a Slow Step

Rate law for a mechanism with a fast initial step: How to determine the rate law for a mechanism with a fast initial step. Remember, the overall rate law must be determined by experiment. Therefore, the rate law must contain no reaction intermediates.