Debye–Hückel equation

https://doi.org/10.1351/goldbook.D01534
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 (I<0.10molkg−1) can be estimated by means of the Debye–Hückel equation: −log10⁡γB=zB2 A I1+a˚ B I where I is ionic strength, z is the charge number of the ion, a˚ is ion size parameter and A and B are temperature-dependent constants. According to the Bates–Guggenheim convention a˚ B is taken to be 1.5molkg−1 at all temperatures and for all compositions of the solutions.
See also: pH
Source:
PAC, 1984, 56, 567. (Physicochemical quantities and units in clinical chemistry with special emphasis on activities and activity coefficients (Recommendations 1983)) on page 569 [Terms] [Paper]
Citation: 'Debye–Hückel equation' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.D01534 RIS BibTex EndNote
Div. VIIPDFTextXMLJSON