The kinetics and mechanism of the oxidation of water by silver(II) in concentrated nitric acid solution

Article abstract of DOI:10.1021/ic50060a015

The kinetics of the oxidation of water by silver(II) in 2.00-6.18 M HNO₃ has been studied between 298.15 and 308.15°K under a variety of conditions. Studies at [Ag(II)] > 1 × 10^-4 M show that the reaction is second order in [Ag(II)] and the observed rate law is -d[Ag(II)]/dt = k_a[Ag(II)]² / k_b + k_d[Ag(I)][H⁺]² = k_II[Ag(II)]² At 6.13-6.17 M HNO₃ and 10⁴[AgO]₀ = 8.33-8.50 M, k_II = 1.78 M^-1 sec^-1 at 298.15°K. The enthalpy of activation for k_II under these concentration conditions is 23.0 ± 0.4 kcal/mole. The proposed mechanism (reactions 1-5) conforms to the observed rate law. The notation [Ag(II)] has been used in place of [AgNO₃⁺] for simplicity. Studies at [Ag(II)] < 1 × 10^-4 M show that there is a first-order reaction with the rate law -d[Ag(II)]/dt = {k_e + k_f[Ag(I)] / (k_r + k_s[Ag(I)])(k_m + k_n[H⁺]₂)} [Ag(II)] = k_I[Ag(II)] At the same temperature and concentration conditions k_II was reported k_I = (2.38 ± 0.10) × 10^-4 sec^-1. The enthalpy of activation, ΔH_I^?, for k_I is 22.3 ± 0.9 kcal/mole. The mechanism proposed (reactions 8-15) involves a free-radical reaction.