A gas can be liquefied by pressure alone when its temperature

A gas can be liquefied if :

A real gas can be liquefied by ?

CO_(2) gas can be liquefied under pressure between

A gas can be liquefied most suitably at .

The essential conditions for liquefaction of gases were discovered by Andrews in 1869 as a result of his study of pressure-volume-temperature relationship for CO_(2) . If was found that above a certain temperature, it was impossible to liquefy a gas whatever the pressure was applied. The temperature below which the gas can be liquefied by the application of pressure alone is called critical temperature (T_(c)) . The pressure required to liquefy a gas at this temperature is called the critical pressure (P_(c)) . The volume occupied by one mole of the substance at the critical temperature and pressure is called critcal volume. Critical constants are related with van der Waals' constant as follows: V_(c) = 3b, P_(c) = (a)/(27b^(2)), T_(c) = (8a)/(27 Rb) Gas A and can be liquefied at room temperature by applying pressure but gas B cannot. This reflects: