| Critical point | Triple point |
|---|---|
| A critical point (or critical state) is the end point of a phase equilibrium . | Triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium . |
| The point at which saturated liquid and saturated vapour lines meet is called the critical point | The point at which fusion line and sublimation line and vapourisation meet is called the triple point |
| It is represented by a point on p-v-T surface | It is represented by a point on p-T diagram but appears as a line on p-v-T surface |
| At critical point there is no distinction between the liquid and vapour phases . below critical point the substances exists in a two phases | At triple point all the three phases can coexist together in equilibrium . |
| An example is example is the liquid-vapor critical point, the end point of the pressure-temperature curve that designates conditions under which a liquid and its vapor can coexist. | The triple point of water is defined to take place at 273.16 K, where K is the SI unit Kelvin. |