JEE Main · 2011 · 10 Apr 2011 · Offline · States of Matter

'a' and 'b' are van der Waals' constants for gases. Chlorine is more easily liquefied than ethane because

(A) $a$ and $b$ for $Cl_{2} < a$ and $b$ for $C_{2} H_{6}$
(B)a for $Cl_{2} < a$ for $C_{2} H_{6}$ but $b$ for $Cl_{2} > b$ for $C_{2} H_{6}$
(C)a for $Cl_{2} > a$ for $C_{2} H_{6}$ but $b$ for $Cl_{2} < b$ for $C_{2} H_{6}$ ✓ Correct
(D) $a$ and $b$ for $Cl_{2} > a$ and $b$ for $C_{2} H_{6}$

Answer: (C)

Solution

How readily a gas liquefies tracks the ratio

\frac{a}{b}

of its van der Waals constants, since

a

measures intermolecular attraction and

b

the molecular size. For chlorine

a \approx 6.49

and

b \approx 0.0562

, while for ethane

a \approx 5.49

and

b \approx 0.0638

. Chlorine thus has the larger

a

and the smaller

b

, hence the bigger

\frac{a}{b}

, so it liquefies more easily than ethane.

JEE Main · 2011 · 10 Apr 2011 · Offline · Single correct option