The kinetics of the oxidation of iodide ions by octacyanomolybdate(V) ions in aqueous solution

Abstract

The kinetics of the reaction 2Mo(CN)83–+ 3I–→ 2Mo(CN)84–+ I3– have been studied as a function of temperature and ionic strength. The reaction is first-order with respect to both the octacyanomolybdate(V) and iodide concentrations and there is evidence of retardation by product octacyanomolybdate(IV). The second-order rate constant is kobs= 3·52 ± 0·13M–1 sec.–1 in the expression –d[Mo(CN)83–]/dt=kobs[Mo(CN)83–][I–] and the activation energy and entropy of activation have the values Ea= 5·68 ± 2·57 kcal./mole and ΔS*=–39 ± 8·5 e.u. at 25·7°C and I= 0·1M. The plot of log kobs against √I is linear with a slope of + 3·12, which suggests that ion-pairs may not play an important role in this reaction.