Isotherms of carbon dioxide gas are shown in Fig. Mark a path for changing gas into liquid such that only one phase (i.e., either a gas or a liquid) exists at any time during the change. Explain how the temperature, volume and pressure should be change to carry out the change.

Isotherms of carbon dioxide gas are shown in Fig. Mark a path for chan

1.	Isotherms of carbon dioxide gas are shown in Fig. Mark a path for changing gas into liquid such that only one phase (i.e., either a gas or a liquid) exists at any time during the change. Explain how the temperature, volume and pressure should be change to carry out the change.
Answer» SOLUTION :It is possible to change a gas into a liquid or a liquid into a gas by a process such that there is a single phase present always. e.g., In figure given above, we can move from A to vertically by increasing the temperature, then we can reach the point by compressing the gas at constant temperature along the isotherm (isotherm at `31.1^(@)C`). The pressure will increase. Now, we can move vertically down D by lowering TEMP. As we cross the H point, we get liquid on critical isotheron. Thus, at no stage during the process, we can through two - phase region. These process is carried out at the TC, in which SUBSTANCE always remains in single phase. This is called continuity of state between the gaseous and the liquid state.