Continuity of State
Continuity of state is the property of transfer of matter between two states especially between gases and liquids by adjusting temperature and pressure maintaining a single phase throughout the process. That means during the transition from one phase (state) to other phase, mixture of phases does not occur at any point.
If you want to convert a certain quantity of gas at the point X, the gas at X on ABCD isotherm is heated till it goes above critical temperature (TC) at a constant volume and the pressure is allowed to increase upto X' and then pressure is maintained constant while the temperature and volume are allowed to fall to Z. The system at Z is now totally in liquid state. This change indicates that a continuous transition takes place in the conversion. Hence, the process of change from gas to liquid or vice-versa is continuous.
