Thermodynamics of solution of SO2(g) in water and of aqueous sulfur dioxide solutions

Abstract

A consistent set of thermochemical property values, Δ_fH°, Δ_fG°, S°, and $C_p^o$, at 298.15 K is given for the known constituents of aqueous sulfur dioxide (${\text{SO}}_2^0(\text{aq})$, ${\text{HSO}}_3^{-}(\text{aq})$, ${\text{SO}}_3^{2-}(\text{aq})$, H⁺(aq), and ${\text{S}}_2{\text{O}}_5^{2-}(\text{aq})$). 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 ${\text{SO}}_2(\text{g})={\text{SO}}_2^0(\text{aq})$, 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 $\mathrm{\Delta }{C}_p^o=155\pm 10\text{J}{\text{mol}}^{-1}{\text{K}}^{-1}$. The standard state partial molar entropy of ${\text{SO}}_3^{2-}(\text{aq})$, 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.