APPARENT MOLAR HEAT-CAPACITIES OF AQUEOUS-SOLUTIONS OF PHOSPHORIC-ACID AND SULFUR-DIOXIDE FROM 303 TO 623 K AND A PRESSURE OF 28 MPA

Heat capacities of aqueous solutions of phosphoric acid from 0.1 to 0. 8 mol-kg(-1) and sulfur dioxide from 0.2 to 0.9 mol-kg(-1) have been m easured with a flow heat-capacity calorimeter from 303 to 623 K and a pressure of 28 MPa. At the lowest molality single-solute solutions as well as mixtures of either H3PO4 or SO2 with HCl were measured to repr ess dissociation. Calculated apparent molar heat capacities were corre cted for dissociation reactions and the chemical relaxation effect. Ex perimental results for mixtures were analyzed using Young's rule. Stan dard state partial molar heat capacities of H3PO4(aq) and SO2(aq) were obtained by extrapolation to infinite dilution. A few measurements of the densities of aqueous H3PO4 and SO2 were made at 25 degrees C and a pressure of 28 MPa.