At , Reaction X has an activation energy of

CHEMISTRY · Single correct · A Level · Chemistry · Kinetics · Kinetics

Problem

At 298 K298\,\text{K}, Reaction X has an activation energy of 45 kJ mol−145\,\text{kJ}\,\text{mol}^{-1}, whereas Reaction Y has an activation energy of 60 kJ mol−160\,\text{kJ}\,\text{mol}^{-1}. No other factors differ between the two reactions. Which statement about their initial rates at 298 K298\,\text{K} is most accurate? (a) The initial rates will be nearly identical because a 15 kJ mol−115\,\text{kJ}\,\text{mol}^{-1} activation-energy difference is negligible compared with the thermal energy available at 298 K298\,\text{K}. (b) Reaction Y will proceed faster because its higher activation energy corresponds to a greater overall energy release. (c) Reaction X will proceed faster because a larger fraction of its molecular collisions can overcome the smaller activation energy. (d) The relative rates cannot be compared without knowing the pre-exponential (frequency) factor in the Arrhenius equation.

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