Solid compound of mixture components

Binary liquid mixtures are known in which the solid that appears when the mixture is cooled is a compound containing both components in a fixed proportion. This kind of solid is called a solid compound, or stoichiometric addition compound. Examples are salt hydrates (salts with fixed numbers of waters of hydration in the formula unit) and certain metal alloys. 

Thermodynamics and Chemistry, second e6Hion,version 3 2011 by Howard DeVoe. Latest version www.chem.umd.edu/thermobook 

The composition of the Uquid mixture in this kind of system is variable, whereas the composition of the solid compound is fixed. Suppose the components are A and B, present in the liquid mixture at mole fractions xa and xb, and the solid compound has the formula AoB. We assume that in the liquid phase the compound is completely dissociated with respect to the components that is, that no molecules of formula AqB exist in the liquid. The reaction equation for the freezing process is 

When equilibrium exists between the liquid and solid phases, the temperature is the freezing point Tf of the liquid. At equilibrium, the molar reaction Gibbs energy defined by ArG = J2iViiii is zero  

Here /ia and ixb refer to chemical potentials in the liquid mixture, and /x(s) refers to the solid compound. 

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