The gas-phase solid catalyzed reaction, 3H2 + N2 + 2NH3
is carried out over an iron catalyst and proceeds by the following mechanism,
H2 + 2S + 2H. S
N2 + 25 + 2N. S
N. S+H. S + HN. S+S
NH. S+HS H2N. S+S
H2N S + H S + NH4+SS
NH3:S + NH3 + S
Derive a rate law assuming that the dissociative adsorption of N2 is the rate limiting step. You may also assume that the dissociative adsorption of H2 is very weak, since this exothermic reaction is carried out at elevated temperatures.