The Elementary Thermodynamics of LSE

Equation 11.1, which we applied to LLE, applies to any phase equilibrium, so it must apply to LSE, with phase 1 being the liquid and phase 2 being the solid. Substituting the definition of the fugacity in terms of the standard state fugacity and solving for the mol fraction of dissolved solid, we find 

If we make that guess, we can also assert that for the pure 1, so Eq. 11.9 becomes 

At the triple pointpi oUd phase = Pi, liquid- If we then assume that we are dealing with low pressures (the vapor pressures of most substances at the triple point are quite low) we may 

A soiid to vapor replaced by Muquid to vapor- We then subtract 

Melting-point data are much more widely available than triple-point data, and for most substances the 1-atm melting-point temperature the triple-point temperature, so it is common to substitute Tmeiting for Tp-ipie point in Eq- H-13, and also to multiply both sides by minus 1, finding 

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