Nitrogen dioxide dimerizes according to the equilibrium reaction
2 NO2(g) ⇌ N2O4(g)
The standard enthalpy change for the forward reaction (formation of N2O4) is ΔH=−57.2kJ mol−1. A kinetic study reports that the potential energy of the transition state for the forward reaction lies 65 kJ above the energy of the reactants.
(a) Using these data, calculate the potential energy of the transition state relative to the products. Show your reasoning.
(b) Draw a fully labeled energy diagram for the forward reaction, including reactants, products, transition state, activation energy for both forward and reverse directions, and ΔH. Your diagram should be to scale in the vertical dimension.
(c) Classify the forward and reverse reactions as endothermic or exothermic, respectively, and justify your classifications quantitatively.
(d) Suppose the same reaction is carried out in the presence of a homogeneous catalyst that lowers the activation energy of the forward reaction by 20 kJ but leaves ΔH unchanged. Explain—without redrawing the entire diagram—how the key features of the energy diagram (activation energies and overall enthalpy change) would be altered.