Because the balanced equation is only a summary of the overall process. Virtually all reactions take place in several steps all of which have different rates. Obviously the overall process can be no faster than the slowest of those steps. Determination of the rate law reveals details of how the overall process takes place.
Answers & Comments
Because the balanced equation is only a summary of the overall process. Virtually all reactions take place in several steps all of which have different rates. Obviously the overall process can be no faster than the slowest of those steps. Determination of the rate law reveals details of how the overall process takes place.