Gaseous ozone undergoes decomposition according to the stochiometric equation: 2O3 (g) → 3O2 (g) Two alternative mechanisms have been proposed to account for this reaction. Mechanism I 2O3 → 3O2 bimolecular, rate constant k Mechanism II O3 ↔ O2 + O fast equilibrium, equilibrium constant K1 O + O3 → 2O2 slow, rate constant k2

A. Derive rate laws for the formation of O2 for each mechanism.

B. Thermodynamic measurements give standard enthalpies of formation for each of the following species at 298 K: species ΔHo 298 (kJ/mol) O2 (g) 0.0 O3 (g) 142.3 O (g) 249.4 The observed activation enthalpy ΔH‡ for the overall reaction 2O3 → 3O2 is 125.5 kJ/mol of O3. Sketch a curve of enthalpy per mol O3 versus reaction coordinate for each of the proposed mechanisms. Label the curves with numerical values for the ΔH between reactants, products, intermediates, and transition states. (Tinoco #33, p.375)

C. Can you exclude either of these mechanisms on the basis of the thermodynamic and activation enthalpy values? Explain your answer.

D. Describe an experiment for distinguishing between the two mechanisms. State clearly the nature of the experiments you would perform and what results you would use to make the distinction. Include in your description what will be measured, what will be varied, and any controls or reference points. (Tinoco #33, p.375)