Two elementary reactions are characterized as follows: • Reaction X: , • Reaction Y:

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

Problem

Two elementary reactions are characterized as follows: • Reaction X: Ea, forward=65 kJ mol−1E_{a,\,\text{forward}} = 65\,\text{kJ}\,\text{mol}^{-1}, ΔE=−40 kJ mol−1\Delta E = -40\,\text{kJ}\,\text{mol}^{-1} • Reaction Y: Ea, forward=90 kJ mol−1E_{a,\,\text{forward}} = 90\,\text{kJ}\,\text{mol}^{-1}, ΔE=−10 kJ mol−1\Delta E = -10\,\text{kJ}\,\text{mol}^{-1} Which statement best predicts how raising the temperature from 300\,K to 400\,K affects the ratio of the forward to reverse rate constants (kf/kr)(k_\text{f}/k_\text{r}) for the two reactions? (a) The ratio decreases for both reactions, and the decrease is larger for Reaction Y than for Reaction X. (b) The ratio increases for both reactions, and the increase is larger for Reaction X than for Reaction Y. (c) The ratio is essentially temperature-independent for both reactions because both forward and reverse rates are multiplied by the same temperature factor. (d) The ratio decreases for both reactions, and the decrease is larger for Reaction X than for Reaction Y.

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