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. Now, if this was not an elementary reaction, we would not be able to use this A and B the way we did here. Now for now, we're only going to worry about elementary reactions. So this is our rate law.