CONDENSED PHASE RULE:

• When a single phase is present i.e (P=1) in two component system i.e (C=2), then the degree of freedom (F) is represented by following equations;

$F=C-P+2$

F= 2 - 1 + 2 ..........(C is component and P is phase therefore by definition P=1 and C=2.......values of C and P are mention in definition)

F= 3

• From the value of F (F=3) we can say that, three variables must be specified in order to describe the condition of phase, i.e. in addition to temperature and pressure the concentration of one of the component has to be given.

   

TRIPLE POINT:

1. Triple Point is the temperature and pressure at which solid, liquid, and vapor phases of a particular substance coexist in equilibrium.
2. In addition to the triple point for solid, liquid, and gas phases, a triple point may involve more than one solid phase, for substances with multiple polymorphs. Helium-4 is a special case that presents a triple point involving two different fluid phases.
3. The triple point of water is used to define the kelvin, the base unit of thermodynamic temperature in the International System of Units (SI)
4. The value of the triple point of water is fixed by definition, rather than measured. The triple points of several substances are used to define points in the ITS-90 international temperature scale, ranging from the triple point of hydrogen (13.8033 K) to the triple point of water (273.16 K, 0.01 °C, or 32.018 °F).
5. It is a specific case of phase equilibrium.