Gases possess characteristic critical temperature which depends upon the magnitude of intermolecular forces between the particles. Following are the critical temperatures of some gases.
Gases H2 He O2 N2
The critical temperature
in Kelvin 33.2 5.3 15 4.3 126
154.3
From the above data what would be the order of liquefaction of these gases? Start writing the order from the gas liquefying first
There are 2 conditions for liquefaction of gases:
• Low temperature
• High pressure
LOW TEMPERATURE: As the temperature of a gas is low, the kinetic energy of the molecule also decreases, which leads volume to get decrease. As the temperature decreases, molecules come close to each other and changes into a liquid.
HIGH PRESSURE: As the pressure increases, makes gas molecule come close to each other and convert into liquid. For each gas, there is a specific temperature above which gas never be liquefied, however, high pressure is applied.
Therefore the effect of temperature is more important than that of pressure.
Liquefaction of so-called permanent gases like dihydrogen, helium is difficult, as they show positive deviation in the value of compressibility. So they require high pressure so that moleculescome close to each other and low the temperature to slow the movement of molecules. These 2 conditions tell about the liquefaction of gases. Therefore O2> N2> H2,> He