A two-step mechanism for the conversion of A to C is summarized by the potential-energy data below (energies are relative to the reactants A):
• Transition state 1: +80 kJ mol⁻¹
• Intermediate B: +20 kJ mol⁻¹
• Transition state 2: +60 kJ mol⁻¹ (measured from the energy of B)
• Product C: –40 kJ mol⁻¹
A homogeneous catalyst lowers the energy of transition state 2 by 30 kJ mol⁻¹ but does not affect any other energy level.
(a) Determine the overall activation energy (relative to reactants) for the uncatalyzed pathway.
(b) Determine the overall activation energy (relative to reactants) for the catalyzed pathway.
(c) Identify the rate-determining step before and after catalysis, and justify your choices using numerical evidence.
(d) Calculate the percentage decrease in the rate-determining energy barrier caused by the catalyst and discuss how this change is expected to influence the rate constant.