Thermodynamics of sulphuric acid: apparent and partial molar heat capacities and volumes of aqueous HSO–4 from 10–55 °C and calculation of the second dissociation constant to 350 °C

Apparent molar heat capacities and volumes of aqueous solutions containing H2SO4 have been determined from 10 to 55°C. These results are complicated by the presence of bisulphate and sulphate ions as well as effects due to chemical relaxation. Consideration of these contributions has led to derived standard-state partial molar heat capacities and volumes for HSO–4 over the stated temperature range. The heat capacity and volume data, which are related to Gibbs free energies by derivatives with respect to temperature and pressure, have been used along with a semi-theoretical model to calculate equilibrium constants for the dissociation of bisulphate to 350°C. Results of these calculations are in good agreement with the best equilibrium data presently available.