The thermodynamic activity of a chemical species or component (ai) is a part of the corresponding chemical potential μ i , according to the relationship:
where μ0 i is the standard state chemical potential at the temperature and pressure of interest, R is the gas constant, and T is the absolute temperature. The activity appears in many important equations pertinent to chemical thermodynamics and chemical kinetics (q.ν.).
The activity and the corresponding standard state chemical potential is always tied to a concentration scale (e.g. Robinson and Stokes, 1965), generally the molal scale for aqueous solutions and the mole fraction scale for all other condensed solutions. The activity is the product of a concentration on that scale and a corresponding activity coefficient. The total chemical potential (on the left hand side of eqn (A19)) is independent of the concentration scale. Changes in the definition of the standard state chemical potential therefore result in changes in the...
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Bibliography
Bates, R.G. (1964) Determination of pH. New York: Wiley and Sons, 425 pp.
Davies, C.W. (1962) Ion Association. London: Butterworths, 190 pp.
Grenthe, I., Fuger, J., Konings, R.J.M. et al. (1992) Chemical Thermodynamics of Uranium, in Chemical Thermodynamics 1 (eds H. Wanner, and I. Forest). Amsterdam: North-Holland, 715 pp.
Guggenheim, E.A. (1935) The specific thermodynamic properties of aqueous solutions of strong electrolytes. Philos. Mag., 19, 588–643.
Harvie, C.E., Möller, N. and Weare, J.H. (1984) The prediction of mineral solubilities in natural waters: the Na–K–Mg–Ca–H–Cl–SO4–OH–HCO3–CO3–CO2–H2O system to high ionic strengths at 25°C. Geochim. Cosmochim. Acta. 48, 723–51.
Helgeson, H.C., Kirkham, D.H. and Flowers, G.C. (1981) Theoretical prediction of the thermodynamic behavior 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. Am. J. Sci., 281, 1249–516.
Mesmer, R.E. (1991) Comments on ‘A new approach to measuring pH in brines and other concentrated electrolytes’ by K.G. Knauss, T.J. Wolery and K.J. Jackson. Geochim. Cosmochim. Acta, 55, 1175–6.
Nordstrom, D.K. and Munoz, J.L. (1985) Geochemical Thermodynamics. Menlo Park, California: The Benjamin/Cummings Publishing Co., 477 pp.
Pitzer, K.S. (1973) Thermodynamics of electrolytes–I. Theoretical basis and general equations. J. Phys. Chem., 77, 268–77.
Pitzer, K.S. (1991) Ion interaction approach: theory and data correlation, in Activity Coefficients in Electrolyte Solutions, 2nd edn (ed. K.S. Pitzer). Boca Raton, FL: CRC Press, pp. 75–153.
Robinson, R. A. and Stokes, R.H. (1965) Electrolyte Solutions (2nd edn, revised). London: Butterworths, 571 pp.
Stokes, R.H. and Robinson, R.A. (1948) Ionic hydration and activity in electrolyte solutions. J. Am. Chem. Soc., 70, 1870–8.
Triolo, R., Grigera, J.R. and Blum, L. (1976) Simple electrolytes in the mean spherical approximation. J. Phys. Chem., 80, 1858–61.
Wolery, T.J. (1990) On the thermodynamic framework of solutions (with special reference to aqueous electrolyte solutions). Am. J. Sci., 290, 296–320.
Wolery, T.J. and Jackson, K.J. (1990) Activity coefficients in aqueous salt solutions. Hydration theory equations, in Chemical Modeling of Aqueous Systems II, ACS Symposium Series 416 (eds Melchior, D.C. and Bassett, R.L.). Washington, DC: American Chemical Society, pp. 16–29.
Cross-references
Rights and permissions
Copyright information
© 1998 Kluwer Academic Publishers
About this entry
Cite this entry
Wolery, T.J. (1998). Activity and activity coefficients. In: Geochemistry. Encyclopedia of Earth Science. Springer, Dordrecht. https://doi.org/10.1007/1-4020-4496-8_5
Download citation
DOI: https://doi.org/10.1007/1-4020-4496-8_5
Publisher Name: Springer, Dordrecht
Print ISBN: 978-0-412-75500-2
Online ISBN: 978-1-4020-4496-0
eBook Packages: Springer Book Archive