Thermodynamics partial molal properties

Calcium-sodium-chloride-type brines (which typically occur in deep-well-injection zones) require sophisticated electrolyte models to calculate their thermodynamic properties. Many parameters for characterizing the partial molal properties of the dissolved constituents in such brines have not been determined. (Molality is a measure of the relative number of solute and solvent particles in a solution and is expressed as the number of gram-molecular weights of solute in 1000 g of solvent.) Precise modeling is limited to relatively low salinities (where many parameters are unnecessary) or to chemically simple systems operating near 25°C. 

Helgeson, H. C. and D. H. Kirkham, 1974, Theoretical prediction of the thermodynamic behavior of aqueous electrolytes at high pressures and temperatures, II. Debye-Hiickel parameters for activity coefficients and relative partial molal properties. American Journal of Science 274, 1199-1261. 

In table 9.14, for the sake of completion, we list the thermodynamic parameters of the HKF model concerning neutral molecules in solution (Shock et al., 1989). Calculation of partial molal properties of solutes (see section 8.11), combined with calculation of thermodynamic properties in gaseous phases (Table 9.5), allows rigorous estimates of the various equilibrium constants at all P and T of interest. 

Shock E. L. and Helgeson H. C. (1990). Calculations of the thermodynamic and transport properties of aqueous species at high pressures and temperatures Standard partial molal properties of organic species. Geochim. Cosmochim. Acta, 54 915-946. 

Shock, E. L., Oelkers, E. H., Johnson, J. W., Sveijensky, D. A. Helgeson, H.C. (1992). Calculation of the thermodynamic behavior of aqueous species at high pressures and temperatures effective electrostatic radii, dissociation constants, and standard partial molal properties to 1000 °C and 5 kb. Journal of the Chemical Society (London) Faraday Transactions, 88, 803—26. 

Tanger, j. C., IV, and H. C. Helgeson. 1988. Calculation of the thermodynamic and transpon properties of aqueous. species at high pressures and temperatures Revised equations of state for the standard partial molal properties of ions and electrolytes. Am. J. Set. 288 19-98. 

Since GE is a thermodynamic property which is additive with respect to RT In Yh it follows that RT In Yt may be considered as a partial molal property. 

Helgeson, H.C., Kirkham, D.H., and Flowers, G.C., 1981, Theoretical prediction of the thermodynamic properties of aqueous electrolytes at high pressures and temperatures IV. Calculation of activity coefficients, osmotic coefficients, and apparent molal and standard and relative partial molal properties to 600°C and 5 kb Amer. Jour. Sci., v. 281, pp. 1249-1493. 

Equation (A-29) holds for all values of A. For A = 1, Eq. (A-29) reduces to Eq. (A-23) and we have completed the proof of Euler s theorem. Equation (A-23) is of use in relating extensive thermodynamic properties to the corresponding partial molal properties. 

Such salt effects are of practical importance in stagemise separation processes and in pollution abatement. Certain salts increase the solubility by more than an order of. magnitude (salting-in), and also change the solvent selectivity for various solutes others decrease the solubility (salting-out) (4, 6, 7, 10) Partial molal properties of the dissolved gas are also profoundly affected by the addition of salt. Thermodynamic properties of gas-electrolyte solution are also an important consideration in the design and operation of fuel cells, where mass transfer of... 

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