Solutions and Activities
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It is important not to lose track of the basic principles of activity amongst all the detailed derivations of the equations. Thus it is appropriate to provide here a brief summary of the salient points of the previous two pages.
Molalities are an alternative way of expressing the composition of a mixture, rather than mole fractions.
We have derived an expression for the general form of the chemical potential of any solvent.
In an ideal solution of two liquids, both components obey Raoult’s Law. However, it has been experimentally observed that, for real solutions at low concentrations, although the solvent (the major component of the solution) usually obeys Raoult’s Law, the solute (the minor component of the solution) does not.
To discuss the thermodynamic properties of liquid mixtures, it is necessary to establish how the chemical potential of a liquid varies with its composition.