Reaction volume and reaction enthalpy upon aqueous peroxodisulfate dissociation: S2O82--> 2SO(4)(center dot-)

The dissociation of aqueous peroxodisulfate induced by laser photolysis at 266 nm has been studied by photoacoustic calorimetry at variable temperatur e. 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 volum e and enthalpy changes, amounting respectively to 8.9 +/- 0.5 ml mol(-1) an d 120 +/- 11 kJ mol(-1). Both results are interpreted as pointing to a diff erential solvation of the involved species.