Re: Phase change equation

The equilibrium lines on phase diagrams are defined by the thermodynamic
equations as applied to mixtures/solutions.  The lines are contours of
equal chemical potential of substances in differing phases in contact. 
The chemical potentials are typically the Gibbs Free Energy. Knowing the
phases and their constituents and being able to construct the correct
expressions of the chemical potentials would enable you do devise truth
scenarious to achieve your purposes.  Indeed, in multicomponent systems
beyond three this is the only way.  However, deriving the chemical
potential expressions is not an elementary matter.

> Torben Laursen wrote:
>
> 
> Do equations for the lines in phase diagrams exist? I want to be able
> to enter a temperature and pressure and test to see which side of the
> line it falls on.