A time-resolved photoacoustic calorimetry study for the determination of the partial volume and formation enthalpy of the aqueous radical

Photoacoustic calorimetry was applied to the photolysis at 266 nm of aqueous peroxodisulfate ion in the presence of bisulfite. A time-resolved analysis of the signals at variable temperature (282–295 K) yields the heat of formation (−530 kJ mol−1) and the partial molal volume (50 mL mol−1) of aqueous sulfite radical. The ca. 11 mL mol−1 difference between the experimental molal volumes of SO 3 - and the parent closed shell ion with similar intrinsic size SO3H−, indicates a diverse rearrangement of the solvent molecules around each species, probably as a result of the dissimilar electronic distribution.