Debye-Hückel Theory

Electrolyte

Debye-Hückel Theory (only valid for dilute solutions)

In electrolyte, the ions are surrounded by clouds of charge opposite their own, due to the attractive forces of the opposing charge. As a result, there is a local excess charge density of one sign opposite to that of the central ion.

The logarithmic mean ionic activity coefficient¹ is proportional to the square root of ionic strength², $\ln f_{\pm}=-A(z_+ z_-)\sqrt{I}$.

Footnote

1. Activity $\equiv$ Activity coefficient $\times$ Molal concentration ↩

2. Ionic strenght $I=\frac{1}{2}\sum_i c_i z^2_i$. ↩