The reaction of compound A to form product D proceeds through the three-step mechanism summarized in the sentence below.
“Step 1 converts A to intermediate B with an enthalpy change of +15 kJ mol⁻¹ and requires an activation energy of 55 kJ mol⁻¹. Step 2 converts B to intermediate C and is exothermic by 25 kJ mol⁻¹ with an activation energy of 40 kJ mol⁻¹. Step 3 converts C to the final product D and is endothermic by 5 kJ mol⁻¹ with an activation energy of 35 kJ mol⁻¹.”
All energies are stated relative to A = 0 kJ mol⁻¹.
(a) Calculate the energy of each intermediate (B and C) relative to A.
(b) Determine the overall enthalpy change, ΔHₒᵥₑᵣₐₗₗ, for the formation of D from A.
(c) Identify the highest-energy transition state on the profile and state its energy relative to A. Explain why this value corresponds to the effective activation energy of the overall reaction.
(d) Sketch a qualitative reaction energy profile on labeled axes that is consistent with the numerical information you have obtained.