Two elementary gas-phase reactions, X → Y (Reaction 1) and X → Z (Reaction 2), are studied at 298 K. The activation energy for Reaction 1 is 35 kJ·mol⁻¹, whereas that for Reaction 2 is 55 kJ·mol⁻¹. No catalysts are present, and both reactions have similar molecular collision frequencies.
Answer the following questions about the relative kinetics of the two reactions at 298 K and after a modest temperature increase.
(a) Identify which reaction proceeds at the faster rate at 298 K. Justify your answer in terms of activation energy.
(b) Describe, at the particulate level, how the distribution of molecular kinetic energies at 298 K accounts for the rate difference you stated in part (a).
(c) The temperature is raised to 308 K. Predict which reaction experiences the larger percentage increase in its rate constant. Explain your reasoning without performing numerical calculations.
(d) Suppose both reactions are carried out instead at 278 K. Explain how the relative rates at 278 K compare with those at 298 K, and discuss any change in the magnitude of the rate ratio between Reaction 1 and Reaction 2.