Two different elementary reactions occur in separate flasks at 298 K. Energy profile descriptions are provided below.
• Reaction C: The energy of the transition state lies 25 kJ·mol⁻¹ above the reactants.
• Reaction D: The energy of the transition state lies 60 kJ·mol⁻¹ above the reactants.
Both reactions are endothermic by 10 kJ·mol⁻¹, and their collision frequencies are comparable.
A chemist raises the temperature of both flasks by the same amount.
(a) Prior to the temperature increase, compare qualitatively the rates of Reaction C and Reaction D. Justify your answer.
(b) After the temperature increase, which reaction’s rate constant experiences the greater fractional change? Explain in terms of activation energy and the fraction of molecules with sufficient kinetic energy.
(c) The chemist observes that, despite equal temperature changes, the absolute rate increase (in mol·L⁻¹·s⁻¹) is larger for Reaction D than for Reaction C. Provide a plausible explanation reconciling this observation with your answer in part (b).