A chemist investigates the decomposition of hydrogen peroxide, 2 H2O2(aq) → 2 H2O(l) + O2(g). The energy profile for the uncatalyzed pathway has an activation energy of 76 kJ mol⁻¹. In a second trial, the same reaction is carried out in the presence of iodide ion, which provides an alternative catalytic pathway with an activation energy of 58 kJ mol⁻¹. Both trials are performed at the same temperature, and all initial concentrations except for the catalyst are identical.
(a) Qualitatively sketch, on the same set of axes, potential energy versus reaction coordinate curves for the catalyzed and uncatalyzed pathways. Clearly label the activation energy for each pathway.
(b) Compare the initial rates of the catalyzed and uncatalyzed reactions. Explain your comparison in terms of the fraction of molecular collisions that are sufficiently energetic.
(c) The chemist also considers raising the temperature of the *uncatalyzed* reaction by 15 °C instead of adding iodide ion. Predict which change—adding the catalyst or raising the temperature—would lead to a greater increase in the reaction rate, and justify your prediction using kinetic principles.
(d) Describe one reason, other than reaction rate, why a chemist might choose to add a catalyst rather than raise the reaction temperature in an industrial setting.