The Rate-Determining Step

For multistep mechanisms, there is often one step that is significantly slower than the other steps. This slowest step is referred to as the rate-determining step, as it limits the rate of the entire reaction. An analogy that illustrates this concept is an hourglass having two different sized openings. The rate of the sand falling to the bottom-most chamber is determined by the smaller of the two openings (Figure 1.1 “Rate-Determining Point in an Hourglass”). Similarly, the rate law of the overall reaction is determined from its rate-determining slowest step.

Figure 1.1.  Rate-Determining Point in an Hourglass

Double hourglass with one opening smaller than the other, which determines rate