Thermodynamic Properties of Aqueous Sulfuric Acid

Thermodynamic properties of aqueous sulfuric acid were modeled with the Pitzer equation. Both the second dissociation constant K-2 for sulfuric acid and the Pitzer parameters were fitted simultaneously. The most accurately considered experimental data including electrochemical cell, osmotic, enthalpy, and vapor pressure data at temperature range (0 to 170) degrees C were used in the assessment. After variations of the used experimental data and the temperature dependency of the Pitzer parameters, the thermodynamic values for the bisulfate dissociation in aqueous sulfuric acid at 25 degrees C were re-evaluated. The obtained values for the dissociation reaction are (11.00 +/- 0.27) and (25.11 +/- 0.80) kJ.mol(-1) for Gibbs energy and enthalpy change, respectively, yielding to 0.0119 for K-2. The obtained thermodynamic values for the cell reactions are in good agreement with CODATA and NBS literature values as well as with other Pitzer based thermodynamic models for aqueous sulfuric acid. The best model selected by using the obtained new thermodynamic data was further tested and compared to the recent Pitzer models with excellent agreement as well as with good extrapolating capabilities with respect to temperature and acid concentration. The total number of fitted terms in Pitzer parameters is eight.