A two-step reaction converts A to D through the mechanism A → B → D. A kinetic study produced the quantitative energy profile described below (all energies are expressed relative to the reactants A).
• Transition state for step 1 (A → B): +85 kJ·mol⁻¹
• Intermediate B: +30 kJ·mol⁻¹
• Transition state for step 2 (B → D): +70 kJ·mol⁻¹
• Products D: –15 kJ·mol⁻¹
Answer the following questions about the reaction.
(a) Calculate the activation energy, E_a, for the forward and the reverse directions of each elementary step.
(b) Determine the overall enthalpy change, ΔH_rxn, for converting A to D.
(c) Based on your calculated activation energies, predict whether the forward or the reverse overall reaction would proceed more rapidly at the same temperature, assuming comparable pre-exponential factors. Explain your reasoning.