The oxidation of iodine to iodate by hydrogen peroxide

Abstract

The kinetics of the oxidation of iodine by hydrogen peroxide, a part of the Bray–Liebhafsky reaction, has been studied between 298 and 323 K using a spectrophotometric method. The rate of reaction passes through a maximum when the concentration of hydrogen peroxide increases. At low hydrogen peroxide concentration, the order of reaction with respect to [I₂] is roughly one, whereas at high hydrogen peroxide concentration the apparent order is higher and there is no simple kinetic law. This reaction can be observed only with sufficient acid and iodate concentrations. However, its rate does not change much with perchloric acid concentration in the range 0.04 to 0.2 mol dm⁻³ and iodate concentration in the range 0.005 to 0.05 mol dm⁻³. The maximum first order rate constant is 8 × 10⁻³ s⁻¹ at 298 K with an activation energy of 80 kJ mol⁻¹. The results are discussed considering a model proposed previously for the Bray–Liebhafsky reaction.