Question

Correct order of value of 'a' for different gases is
(1) Ar <CO < N2
(2) CH4 < NH3 < SO2
(3) NH3 < Cl2< HCI
(4) SO2 < CO2 <H2​

Answer 1

The correct order of 'a' for different gases is :

(2) CH4 < NH3 < SO2

• 'a' is known as correction term for attraction in the vanderwaal equation .

• Higher value of 'a' represents higher intermolecular force of attraction . Which means easier liquification of gases.

• In SO2 the attractive force present is dipole-dipole forces as it is angular molecules and polar.

• In NH3 the attractive force present is hydrogen bonds .

• In CH4 the attractive force present is London dispersion forces as non polar due to similar electronegativity difference between C and H.

• So, as in SO2 more attraction so more 'a' value while in CH4 less attraction so less 'a' value.

• 'a' value for SO2 = 6.865 L²/mol² , NH3= 4.225 L²/mol² , CH4= 2.3 L²/mol².

• So, the order is (2) CH4 < NH3 < SO2.