Liquefaction of gases
Define critical temperature. Give
examples.
Ans. The temperature of a gas above
which a gas cannot be liquefied, no matter how great the pressure is applied, is called critical temperature. It is denoted by Tc.
Examples:
Gas Critical temperature (oC) O2 -118.7 NH3 132.4 CO2 31.1
Define critical pressure. Give
examples.
Ans. It is the minimum pressure
which is required to liquefy a gas at its critical temperature. It is denoted
by Pc.
Examples:
Gas Critical pressure (atm) O2 49.7 NH3 111.5 CO2 73.0
Define critical volume. Give
examples.
Ans. The volume which is occupied by
one mole of a gas at critical temperature and critical pressure is called
critical volume. It is denoted by Vc.
Examples: The critical volume of O2
is 74.42 cm3 mol-1.
How the critical temperature is an
essential criteria to be considered for the liquefaction of gases?
Ans. At low temperature and at high
pressure gases can be converted into liquid. The temperature of gas should be
equal or less than critical temperature to change gas into liquid. Above
critical temperature gas cannot be converted into liquid, how much the pressure
is applied.
What is Joule-Thomson effect?
Ans. When compressed gases are allowed to expand suddenly into
region of low pressure, cooling takes place, it is called Joule-Thomson effect.
In Joule-Thomson effect sudden
expansion of the gas molecules needs energy. Why?
Ans. In compressed state, sufficient
attractive forces present between the molecules of gas. Therefore, in
Joule-Thomson effect sudden expansion of the gas molecules needs energy to
overcome the intermolecular forces.
Joule-Thomson effect is operative in
the Linde’s method of liquefaction of air. How ?
Ans. In Linde’s method the gas is compressed
to 200 atmospheric pressure. These compressed gases are suddenly allowed to
expand through a nozzle. This sudden expansion of the gas and the consequent
cooling is called Joule-Thomson effect and this effect is operative in Linde’s
method of liquefaction.
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