Question

Consider the van der Waals constants, a and b, for the following gases.

Gas	Ar	Ne	Kr	Xe
$a/(atmd{m}^{6}mo{l}^{-2}$	1.3	0.2	5.1	4.1
$b/(10^{-2}d{m}^{3}mo{l}^{-1}$	3.2	1.7	1.0	5.0

Which gas is expected to have the highest critical temperature?

• A. Kr
• B. Ne
• C. Ar
• D. Xe

Answer 1

Answer: (A)

$T_c=\frac{8a}{27Rb}$
Greater value of $\frac{a}{b}\Rightarrow$ higher is 'T${}_c$'
Gas $a/b$
Ar $\frac{1.3}{3.2}=0.406$
Ne $\frac{0.2}{1.7}=0.118$
Kr $\frac{5.1}{1}=5.1$
Xe $\frac{4.1}{5}=0.82$
$\therefore T_c$ has order : $Kr>Xe>Ar>Ne$