Kinetics of Oxygen Exchange between Selenate Ions and Water

Abstract

Abstract The rate of oxygen exchange between selenate ions and solvent water has been measured by using oxygen-18 as a tracer. At 30°C in the concentration range of [H2SeO4]=0.57–1.5 M, and at 80°C in the region of pH=1.0–2.3, the rate may be expressed as R=k1[H+][HSeO4−]. The values of the energy and entropy of activation are 23.1 kcal/mol and −5.0 e.u.(80°C) at pH=1.12, and 21.8 kcal/mol and −9.9 e.u.(30°C) at [H2SeO4]=1.64 M. An A–2 mechanism has been suggested for this path. Above ca 1.5 M H2SeO4, an additional rate term proportional to [H2SeO4]2 comes into play.