Aqueous hydrogen peroxide, H2O2(aq), decomposes slowly at room temperature to form O2(g) and H2O(l). A chemist adds a small amount of iodide ion, I−(aq), which is known to catalyze the reaction. A verbal description of the potential-energy profiles for the two pathways is provided below.
• The uncatalyzed pathway exhibits a single transition state that lies 76 kJ mol−1 above the reactants.
• The catalyzed pathway proceeds through two elementary steps separated by an intermediate. The highest‐energy transition state on the catalyzed surface lies 42 kJ mol−1 above the reactants.
Assume that the concentrations of all species other than the catalyst are identical for the two pathways.
(a) Describe, in terms of molecular collisions and activation energy, why the catalyzed reaction proceeds at a faster rate than the uncatalyzed reaction at 298 K.
(b) Iodide ion is consumed in the slow step and regenerated in a subsequent step. Explain how this observation is consistent with the definition of a catalyst, and identify the role of the intermediate in maintaining a constant net concentration of I−.
(c) Using the information in the potential-energy profiles, explain why the relative rate enhancement provided by the catalyst is expected to be greater at 298 K than at 500 K.