So now let's suppose we have the following elementary reaction in which our reactants x and y convert to our product z and W. Now, A-B-C and D are the coefficients that represent the moles of each respective atom. Now let's suppose our reaction is a dynamic equilibrium. And what that basically means once again is that the rates at which x and Y are converting to z and W is the same as the rate at which z and w is converting to x and Y. Now, once again, we're making an assumption that this is elementary reaction. So that means we can write the rate law for each reaction going this way and going that way by simply using the coefficient ADC and d.
So let's do exactly that. So the rate of our four reaction is equal to the constant for going this way.