Now, we're only going to worry about the forward reaction, but know that if there is a forward reaction, there could also be a reverse reaction. Now let's look at the rate law. The rate law is this entire equation or relation. So rate of the forward reaction of this reaction is given by our rate constant KF for the forward reaction times the concentration of X to the A power. In this case this A times the concentration of Y to the B power B. Now, the reason we chose A and B is because this is an elementary reaction.