Discuss triple point in one component system
TRIPLE POINT:- The three curves OA, 08, and OC meet at 0 at which solid, liquid and vapour co-exist in equilibrium. This point at 273. 16K (0.0075°C} and 4.58 mm of Hg pressure is called Triple point. The system is invariant.
F=C·P+2 ∴ F=3-P=3-3=0 ∴ =O
This means the degree of freedom is zero therefore neither pressure nor temperature can be changed without causing the disappearance of one of the phases. If either temperature or pressure is changed even slightly, one of the three phases disappears and the system changes from non-varient to univariant.