For real gases the relation between p, V and T is given by van der Waals equation : (p+(an^(2))/(V^(2)))(V-nb)=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 magnitude of intermolecular attraction. (i) Arrange the following gases in the increasing order of 'b'. Give reason. O_(2),CO_(2),H_(2),He (ii) Arrange the following gases in the decreasing order of magnitude of 'a'. Give reason. CH_(4),O_(2),H_(2)

For real gases the relation between p, V and T is given by van der Waa

1.	For real gases the relation between p, V and T is given by van der Waals equation : (p+(an^(2))/(V^(2)))(V-nb)=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 magnitude of intermolecular attraction. (i) Arrange the following gases in the increasing order of 'b'. Give reason. O_(2),CO_(2),H_(2),He (ii) Arrange the following gases in the decreasing order of magnitude of 'a'. Give reason. CH_(4),O_(2),H_(2)
Answer» Solution :(i) As 'b' REPRESENTS molar volume occupied by the gas molecules, GREATER the size of the molecules, greater is the volume occupied by 1 mole of molecules. The size and hence the value of 'b' increase in the order : `H_(2) lt He lt O_(2) lt CO_(2)` (ii) As all the given molecules are non-polar, the magnitude of intermolecular attractions and hence the value of 'a' increase with the increase in numberof electrons in the MOLECULE, i.e., in the order : `CH_(4) gt O_(2) gt H_(2)` (Greater the number of electrons, greater is the size of electron cloud, greater is the polarisation of the molecule, greater is the attraction).