Dependence of equilibrium constants on ionic strength

The relation between K and the ionic strength should be worked out for each given reaction. The argument will be given for the reaction used previously to derive the algebraic form of the equilibrium constant (see Section 8.14). 

This is a quotient of activities and thus is an ideal equilibrium constant. 

The Debye-Huckel theory can be used to express activity coefficients in terms of the ionic strength of the solution. 

From this it is clear that the equilibrium constant expressed in concentrations, i.e. A non-ideai is not a tme constant but depends on the particular ionic strength at which the measurements are made. This applies, in particular, to any equilibrium which involves charged species or charge-separated species, since these are more likely to cause non-ideality than molecular species. All concentration equilibrium constants should thus be corrected for non-ideality. 

There are two main ways of doing this, and both require use of the Debye-Hiickel theory. 

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