![]() The absence of the symbol “ ^ “ over a quantity implies that the quantity is stoichiometric. The symbol “ ^ “ denotes a quantity which pertains to a species as distinct from a stoichiometric quantity. In the above equations, a ^ i is the activity of the i th species which is equal to the quantity m ^ i γ ^ i where m ^ i and γ ^ i are, respectively, the molality and activity coefficient of that species. The final uncertainties are adjusted to reflect the agreement or lack of it between the various data sets. A final set of values for both the processes and thermodynamic properties is then selected which provides a “best” fit to all of the available data. The approach adopted in this paper is to select a tentative set of values and accompanying uncertainties for the various processes involving sulfur (IV)-oxygen species and then to examine the various thermodynamic pathways for consistency. They include calorimetric measurements of heat capacities and enthalpies of solution and reaction, measured equilibrium constants, entropies, solubilities, and vapor pressure measurements (both partial and total) over aqueous solutions. Thermodynamic data from a wide variety of measurement techniques are considered. All auxiliary thermochemical data have been taken from the most recent set of CODATA key values which were converted, where appropriate, to a standard state pressure of one bar (0.1 MPa). ![]() Throughout this paper we are adhering to the standard states and units used in the NBS Tables of Chemical Thermodynamic Properties 2. Also included are values of the activity and osmotic coefficients, the relative apparent molar enthalpy ( L ϕ) as a function of concentration, and the partial pressure of SO 2(g) over its aqueous solution. A consistent set of property values 1, Δ f H°, Δ f G°, S°, and C p o at 298.15, is given for these species which results from the evaluation of the various processes involving them. The aqueous species of relevance to this study are neutral aqueous sulfur dioxide SO 2 0 ( aq ), bisulfite ion HSO 3 − ( aq ), sulfite ion SO 3 2 − ( aq ), pyrosulfite ion S 2 O 5 2 − ( aq ), and H +(aq). This study was performed as part of the analysis of the thermodynamics of sulfur and its compounds. The purpose of this paper is to present the results of an analysis of the thermodynamic properties of the SO 2 + H 2O system. Parameters are given which extend the predictions to temperatures up to 373 K. The standard state partial molar entropy of SO 3 2 − ( aq ), obtained by the analysis of data via two independent thermodynamic pathways is −15.40☐.80 J mol −1 K −l at 298.15 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). 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 SO 2 for the temperature range 278 to 393 K. Also tabulated are values of the mean ionic activity coefficients, osmotic coefficients, partial pressure of SO 2(g), and the relative apparent molar enthalpy as a function of concentration of SO 2(aq) at 298.15 K. ![]() 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 ( SO 2 0 ( aq ), HSO 3 − ( aq ), SO 3 2 − ( aq ), H +(aq), and S 2 O 5 2 − ( aq )).
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