Researchers propose the following mechanism for the synthesis of compound P from starting material L.
Step 1 (fast, reversible) L ⇌ C ΔH₁ = +5 kJ mol⁻¹, Ea,forward = 35 kJ mol⁻¹, Ea,reverse = 30 kJ mol⁻¹
Step 2 (slow) C → D ΔH₂ = +20 kJ mol⁻¹, Ea = 90 kJ mol⁻¹
Step 3 (fast) D → P ΔH₃ = –140 kJ mol⁻¹, Ea = 25 kJ mol⁻¹
The overall enthalpy change for the conversion of L to P is –115 kJ mol⁻¹.
Answer the questions that follow.
(1) Part 1: (a) Construct a qualitative reaction energy profile consistent with the data above. Clearly label all reactants, intermediates, products, and transition states, and indicate the relative heights of the activation barriers.
(2) Part 2: (b) Identify the transition state with the highest potential energy on your profile and explain how this determines the overall rate of formation of P.
(3) Part 3: (c) Propose a strategy (other than increasing temperature) that could accelerate the overall reaction rate. Identify which elementary step your strategy targets and justify how it would affect the energy profile you drew in part (a).
(4) Part 4: (d) Evaluate whether selectively lowering the activation energy for Step 1 (without altering Steps 2 and 3) would significantly increase the overall rate of formation of P. Support your argument with reasoning based on the profile.