Thermodynamics of proton dissociation from aqueous bicarbonate: apparent molar volumes and apparent molar heat capacities of potassium carbonate and potassium bicarbonate at T=(278.15 to 393.15) K and at the pressure 0.35 MPa

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We have determined the apparent molar volumes V φ and apparent molar heat capacities C p, φ of aqueous potassium carbonate and potassium bicarbonate solutions in the ranges (0.014⩽ m/(mol · kg −1)⩽0.51) and (278.15⩽ T/K⩽393.15) at the pressure p=0.35 MPa. Corrections for speciation due to hydrolysis and disproportionation in solution were applied using Young's rule, and semi-empirical equations representing ( V φ , m, T) and ( C p, φ , m, T) for the species {2K +, CO 3 2−(aq)} and {K +, HCO 3 −(aq)} were fitted to the experimental results. We have used these equations to estimate the change in volume Δ r V m, change in heat capacity Δ r C p,m, enthalpy change Δ r H m, entropy change Δ r S m, and equilibrium molality quotient pQ for the second proton dissociation reaction from aqueous carbonic acid.