Critical Evaluation of the Second Dissociation Constants for Aqueous Sulfuric Acid over a Wide Temperature Range

The scope of this article is to study the ability of different equations for K-2 and different sets of Pitzer parameters to model the thermodynamic properties of the H2SO4-H2O system over a wide temperature range. Three Pitzer parameters are found essential in modeling aqueous sulfuric acid, namely, C-phi for H+/SO42- interaction and parameters beta((0)) and beta((1)) for H+/HSO4- interaction. Several thermodynamic models with different K-2-equations consisting of only four Pitzer parameters, the mentioned three parameters extended by beta(0) for H+/SO42- interaction with simple temperature dependency (a + b/T), can describe stoichiometric activity and osmotic coefficients as well as vapor pressure of aqueous sulfuric acid up to a 6 molal solution in the temperature range (0 to 170) degrees C with good to moderate extrapolation capabilities. Increasing the number of parameters above four do not improve the assessment. The predicted values with different K-2-equations are assumed experimentally accurate. One of the four parameters models, Hepler A, can predict the apparent heat of solution in the temperature range (0 to 50) degrees C with reasonable accuracy even though no enthalpy or heat capacity data were included in the assessment.