Thermodynamics of Solution of SO2(g) in Water and of Aqueous Sulfur Dioxide Solutions.

Abstract

A consistent set of thermochemical property values, Δ _f H°, Δ _f G°, S°, and $C_p^o$ , at 298.15 K is given for the known constituents of aqueous sulfur dioxide ( ${\text{SO}}_2^0\left(\text{aq}\right)$ , ${\text{HSO}}_3^{-}\left(\text{aq}\right)$ , ${\text{SO}}_3^{2-}\left(\text{aq}\right)$ , H⁺(aq), and ${\text{S}}_2{\text{O}}_5^{2-}\left(\text{aq}\right)$ ). Also tabulated are values of the mean ionic activity coefficients, osmotic coefficients, partial pressure of SO₂(g), and the relative apparent molar enthalpy as a function of concentration of SO₂(aq) at 298.15 K. The data analysis considered a wide variety of measurement techniques: calorimetric enthalpies of solution and reaction, heat capacities, equilibrium constants, solubilities, and vapor pressure measurements, both partial and total, over aqueous solutions of SO₂ for the temperature range 278 to 393 K. All auxiliary data have been taken from the most recent set of CODATA values which were converted to a standard state pressure of one bar (0.1 MPa). For the process ${\text{SO}}_2\left(\text{g}\right)={\text{SO}}_2^0\left(\text{aq}\right)$ , the selected "best" values are: K = 1.23±0.05 mol kg^-1 bar^-1, ΔG° = -0.5±0.10 kJ mol^-1, ΔH° = -26.97±0.30 kJ mol^-1, and $\Delta C_p^o=155\pm 10\text{J}{\text{mol}}^{-1}{\text{K}}^{-1}$ . The standard state partial molar entropy of ${\text{SO}}_3^{2-}\left(\text{aq}\right)$ , obtained by the analysis of data via two independent thermodynamic pathways is -15.40±0.80 J mol^-1 K^-l at 298.15 K. Parameters are given which extend the predictions to temperatures up to 373 K.