Question

The rate law for the main reaction? Please Explain

Answer 1

for any proposed reaction mechanism slowest step is the rate determining step; the rate law for this step is same to that of overall rate law for main reaction (P→R).

hence rate of the reaction=K3[Q]²[P] (according to step 2)........(i)
but Q is only an unstable intermediate, that is why we have to replace it.
so according to first step the Equilibrium constant Keq=$\frac{K1}{K2}$=$\frac{[Q] ^{2} }{[P]}$
∴[Q]²=[P].(K1/K2)........................................................................(ii)
using the equation (ii) putting the value of [Q]² in equation (i)we get
rate of the reaction=K3*[P]*(K1/K2)*[P]
                              =(K1*K3/K2)*[P]