The rate expression for a heterogenous catalytic reaction is given by, - r_{A} = K.K_{A}P_{A}(1 + K_{A}.P_{A} + K_{R}.P_{R}), where K is surface reaction rate constant and K_{A} and K_{R} are absorption equilibrium constants of A and R respectively. If K_{R}P_{R} >> (1 + K_{A}P_{A}), the apparent activation energy E_{A} is equal to (given E is the activation energy for the reaction and ΔH_{R} and ΔH_{A} are the activation energies of adsorption of R and A)