hi can you please explain IN DETAILS the topic of liquification of gases and the graph of isotherms of carbon dioxide at various temperatures in the ncert text book on page 147...
A gas can be liquefied by increasing its pressure and decreasing its temperature.
The said graph is a result of an experimental measurement of volumes of carbon dioxide samples at different pressures keeping the temperature constant each time.
The plots of P vs V at different temperatures are called the isotherms. The said isotherm is of carbon dioxide. As you have studied there are mainly three regions marked in the graph. These are shown in purple, pink and white colors.
The purple colored region indicates the existence of CO2 in liquid state. The pink colored region indicates the existence of equilibrium between the liquid and the vapor state of CO2. The white colored region indicates the existence of CO2 in vapor state. The interpretation of the graph is as follows:
( i.) At high temperature the isotherm looks like that of an ideal gas and no liquefaction occurs (irrespective of high pressure).
( ii.) As the temperature is lowered the shape of the curve changes and there occurs a considerable deviation from the ideal behavior. At a temperature of 30.98oC, CO2 remains a gas till 73 atm. At this point liquid CO2 appears for the first time. This temperature is called the critical temperature of carbon dioxide and is denoted as Tc. The volume at this point is denoted as Vc and the pressure is Pc. An increase of pressure beyond 73 atm causes compression of liquid carbon dioxide.
( iii.) At 21.5oC, CO2 remains as gas upto point F. Further compression does not alter the pressure but volume decreases till point G is reached. In fact, there exists liquid vapor equilibrium along the horizontal line FG. At point G all the gas gets condensed. The line GH represents the compressibility of liquid CO2.
( iv.) The points A, E, J represent gaseous states while the points L, H, D represent liquid state. I hope, with these points you can conclude that: At critical point, the surface of separation (boundary) between liquid and gas phase disappears and the liquid changes to gaseous state continuously.