Assume the elementary steps for this reaction are the following: Step 1: Slow \ (A + A \rightarrow C + E\) (with a rate constant, \ (k_1\)). Step 2: Fast \ (E + B \rightarrow A + D\) (with a rate constant, \ (k_2\)). In chemical kinetics, the overall rate of a reaction is often approximately determined by the slowest step, known as the rate-determining step (RDS) or rate-limiting step. For a given reaction mechanism, the prediction of the corresponding rate equation (for comparison with the experimental rate law) is often simplified by using this approximation of the rate-determining step. Rate-Determining Step. The determination of a reaction mechanism can only be made in the laboratory. When a reaction occurs in a sequence of elementary steps, the overall reaction rate is governed by whichever one of those steps is the slowest. The rate-determining step is the slowest step in the sequence of steps in a reaction mechanism. To get an idea of how one step is rate determining, imagine driving on a one-lane road where it is not possible to pass another vehicle.