THE EFFECT OF TEMPERATURE AND PRESSURE ON THE PROTONATION OF O-PHOSPHATE IONS AT 348.15 AND 398.15-K, AND AT 1.52 AND 12.50-MPA

Flow calorimetry has been used to study the interaction of HPO42- and H2PO4- with H+ in water at temperatures of 348.15 and 398.15 K and at pressures of 1.52 and 12.50 MPa. The protonations of HPO42- and H2PO4- are exothermic and endothermic, respectively, under these experimenta l conditions. Under the conditions of this study, the effect of pressu re on the enthalpy changes for both reactions is small. Equilibrium co nstant K, enthalpy change DELTAH, and entropy change DELTAS values are given for the protonation reactions at each temperature. These values are compared with those reported in the literature. Incorporation int o the calculation procedure of reactions involving association between protonated phosphate species to form hydrogen-bonded dimers does not result in better fits of the experimental data.