A chemist investigates the catalytic decomposition of N2O(g) to N2(g) + ½ O2(g). The uncatalyzed pathway consists of two elementary steps with the following energies relative to the reactants:
• Step 1: Transition state at +150 kJ mol⁻¹ → Intermediate at +40 kJ mol⁻¹
• Step 2: Transition state at +180 kJ mol⁻¹ → Products at –90 kJ mol⁻¹
A heterogeneous catalyst selectively lowers the energy of the second transition state by 60 kJ mol⁻¹ but leaves all other energy levels unchanged.
(a) Sketch or describe in words the original uncatalyzed potential-energy diagram and then the catalyzed diagram on the same relative energy scale.
(b) For both the uncatalyzed and catalyzed reactions, determine the overall activation energy (defined as the energy difference between the reactants and the highest transition state).
(c) Explain qualitatively how the catalyst affects the rate of the overall reaction and whether it alters the reaction enthalpy, ΔH. Support your answer with references to the energy values supplied.
(d) Predict how the presence of the catalyst would influence the value of the equilibrium constant, K, for the decomposition at a fixed temperature and justify your prediction.