## Wikipedia - Debye–Hückel equation Debye–Hückel equation

https://doi.org/10.1351/goldbook.D01534
The @C01032@ 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 @E01945@ 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 @M03969@ activity @C01124@ of the chloride ion in dilute aqueous solutions ($$I < 0.10\ \text{mol kg}^{-1}$$) can be estimated by means of the @D01533@–Hückel equation: $-\log _{10}\gamma _{\text{B}}=\frac{z_{\text{B}}^{2}\ A\ \sqrt{I}}{1 + \mathring{a}\ B\ \sqrt{I}}$ where $$I$$ is @I03180@, $$z$$ is the @C00993@ of the ion, $$\mathring{a}$$ is ion size parameter and $$A$$ and $$B$$ are temperature-dependent constants. According to the @B00617@ $$\mathring{a}\ B$$ is taken to be $$1.5\ \sqrt{\text{mol kg}^{-1}}$$ at all temperatures and for all compositions of the solutions.