For real gases the relation between p, V and T are given by van der Waals equation:
P + an2(V – nb) / V2= nRT
Where‘a’ and ‘b’ are van der Waals constants, ‘nb’ is approximately equal to the total volume of the molecules of a gas.
‘a’ is the measure of the magnitude of intermolecular attraction.
(i) Arrange the following gases in the increasing order of ‘b’. Give reason. O2, CO2, H2, He
(ii) Arrange the following gases in the decreasing order of magnitude of ‘a’. Give reason. CH4, O2, H2
(i) the increasing order of ‘b’ is as follows:
He < H2< O2< CO2 As the Vander Waals constants,‘b’ is approximately equal to the total volume of the molecules of a gas.
(ii)The decreasing order will be:
CH4> O2> H2 as the surface area of CH4 is highest so, it has highest Vander Waal’s force of attraction so, has the highest value of ‘a’, followed by O2 and H2.