Why can we ignore other steps and use only the rate-determining step in a mechanism to write the predicted rate law?

A reaction mechanism is a series of elementary steps that describe the pathway of a chemical reaction. Each elementary step involves a small number of reactants (usually one or two) coming together and reorganizing their bonds to give the intermediate products and eventually the final products.

The rate-determining step is the slowest step in a reaction mechanism. It has the highest energy barrier (activation energy) to be overcome, which determines the overall rate of the reaction. The other steps in the reaction mechanism are faster and do not significantly affect the reaction rate.

A rate law is an expression that relates the rate of a chemical reaction to the concentrations of the reactants. The overall rate law for a reaction mechanism is determined by the step with the slowest rate, as this controls the overall rate of the reaction.

Since the rate-determining step is the slowest and controls the overall reaction rate, it is the primary focus when writing the predicted rate law. The other steps in the reaction mechanism are faster and do not limit the overall reaction rate. Therefore, they have minimal impact on the rate law and can be ignored. Here is an analogy to help understand the concept: Imagine a series of cars on a highway, where one of them is driving at a significantly slower speed than the others. This slow car dictates the speed at which the cars behind it can travel, regardless of how fast the other cars can potentially go. Similarly, in a reaction mechanism, the rate-determining step acts like the slow car, determining the overall pace at which the reaction proceeds. Since the other steps are faster and do not dictate the reaction rate, they can be ignored when writing the predicted rate law.