Question

The van der Waal's coefficient of the inert gases $He,Ar$ and $Xe$ are given below:

Inert Gas	$a\left(atmd{m}^{6}mo{l}^{-2}\right)$	$b\left({10}^{-2}d{m}^{3}mo{l}^{-1}\right)$
$He$	$0.34$	$2.38$
$Ar$	$1.337$	$3.20$
$Xe$	$4.137$	$5.16$

Choose the appropriate pair to complete the following statement. "The increase in the value of ${}^{\prime }{a}^{\prime }$ signifies the increasing importance of ..... interaction while increase in the value of ${}^{\prime }{b}^{\prime }$ is due to ....."

• A. Ion-ion; increased atomic volume
• B. Induced dipole-induced dipole; increased atomic volume
• C. Induced dipole-dipole; dipole-dipole interaction
• D. Dipole-dipole; decreasing ionization energies

Answer 1

Answer: (B)

Induced dipole-induced dipole; increased atomic volume

"The increase in the value of ′a′ signifies the increasing importance of induced dipole-induced dipole interaction while increase in the value of ′b′ is due to increased atomic volume.
As we go down the group of noble gases, with increase in atomic size, the polarisabiity of atoms of inert gas increases. The dipoles are easily induced. Due to this, the extent of induced dipole-induced dipole interactions increases. The intermoleular forces becomes stronger. This increases the value of a.
'a' is a proportionality constant called coefficient of attraction. It refers to the pressure correction. Its value depends on the nature of the gas. It corrects for the attractive forces present in a real gas in the van der Waals' equation.
The term 'nb' refers to volume correction.