For real gases van der Waals equation is written as
\(\Big(p + \frac{an^2}{V^2}\Big)\)(V - nb) = nRT
where ‘a’ and ‘b’ are van der Waals constants.
Two sets of gases are:
(I) O2, CO2, H2 and He
(II) CH4, O2 and H2
The gases given in set-I in increasing order of ‘b’ and gases given in set-II in decreasing order of ‘a’, are arranged below. Select the correct order from the following :
(a) (I) He < H2 < CO2 < O2 (II) CH4 > H2 > O2
(b) (I) O2 < He < H2 < CO2 (II) H2 > O2 > CH4
(c) (I) He < H2 < O2 < CO2 (II) CH4 > O2 > H2
(d) (I) H2 < O2 < He < CO2 (II) O2 > CH4 > H2
Correct answer: (c) (I) He < H2 < O2 < CO2 (II) CH4 > O2 > H2
Explanation:
Molar mass ↑, 'a' increases
size of molecule ↑, 'b' increases
b(L/mol)
H2 → 0.02661
He → 0.0237
O2 → 0.03183
CO2 → 0.04267
a(bar L2/mol2)
CH4 → 2.25
O2 → 1.36
H2 → 0.244