...
It means that 3-phase equilibrium (solid, liquid an gas) has zero degrees of freedom :
and thus making a single point on Phase Equilibrium Diagram (called triple point )LaTeX Math Inline body F = 0
can only exist at fixed Temperature and Pressure, called Triple Point.
The 2-phase equilibrium has one degree of freedom:
1 and LaTeX Math Inline body F=
and form a smooth line line on Phase Equilibrium Diagram.1
See also
...
Natural Science / Physics / Thermodynamics / Thermodynamic system / Phase / Phase Equilibrium
...