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) °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°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.