Reaction volume and reaction enthalpy upon aqueous peroxodisulfate dissociation:: S2O82-→2SO4•-

The dissociation of aqueous peroxodisulfate induced by laser photolysis at 266 nm has been studied by photoacoustic calorimetry at variable temperature. Data treatment considered the temperature dependence of reaction quantum yields and the difference of thermal expansivities between the sample and the calorimetric reference solutions. The method yielded the reaction volume and enthalpy changes, amounting respectively to 8.9 +/- 0.5 ml mol(-1) and 120 +/- 11 kJ mol(-1). Both results are interpreted as pointing to a differential solvation of the involved species.