Thermal Properties of Dilute Solutions

A dilute solution typically means a solution containing no more than about 10 mol 1 of solute. For the solvent, a convenient reference state is its own pure liquid state at 1 bar. However, a more useful reference state for the solute, including aqueous solutions of electrolytes and non-electrolytes, is that of infinite dilution in the solvent 

The general form of the chemical potential of a real solute in a binary solution of 

The interactions between ions contained in an ionic solution are so strong that the solution approaches ideahty in the sense of obeying Henry s law only at very low values of total ion concentration, usually less than 10 mol kg [68, 69]. In precise considerations, ion activities must be used. In the case of strong electrolytes 

Now both types of ion share equal responsibility for the non-ideality. 

Strong and long-range Coulombic forces acting between ions are primarily responsible for the departures from ideality (the activity coefficients are lowered) and dominate all other contributions. The effect has been evaluated in the Debye-Htickel theory and there exist several equations, which are useful in estimating the mean activity coefficient [68, 69]. The latter is related to the ionic strength of the solution  

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