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Debye–Hückel equation

The chemical potential or activity of ions cannot be determined on a purely thermodynamic basis. This is due to the fact that the effects of an ion cannot be separated from the effects of the accompanying counter-ion, or in other terms, the electrochemical potential of the ion cannot be separated into the chemical and the electrical component. Such a separation must necessarily be based on a non-thermodynamic convention. The present convention is based on the assumption that the molal activity coefficient of the chloride ion in dilute aqueous solutions (Math - ei) can be estimated by means of the Debye–Hückel equation:
Math - e
where Math - text is ionic strength, Math - text is the charge number of the ion, Math - text is ion size parameter and Math - text and Math - text are temperature-dependent constants. According to the Bates–Guggenheim conventionMath - text is taken to be Math - ei at all temperatures and for all compositions of the solutions.
See also: pH
PAC, 1984, 56, 567 (Physicochemical quantities and units in clinical chemistry with special emphasis on activities and activity coefficients (Recommendations 1983)) on page 569
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IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A.Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
Last update: 2008-10-07; version: 2.0.2.
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