JEE Advanced · 2009 · 12 Apr 2009 · Paper 1 · States of Matter

The term that corrects for the attractive forces present in a real gas in the van der Waals equation is

(A) $nb$
(B) $\frac{a n ^{2}}{V ^{2}}$ ✓ Correct
(C) $- \frac{a n ^{2}}{V ^{2}}$
(D) $- nb$

Answer: (B)

Solution

The van der Waals equation for real gases is:

(P + \frac{n ^{2} a}{V ^{2}}) (V - nb) = n R T

The term

\frac{n ^{2} a}{V ^{2}}

is added to the pressure to correct for the attractive forces between gas molecules. This term represents the pressure reduction due to intermolecular attractions.

The term

nb

corrects for the volume occupied by the gas molecules themselves (excluded volume).

Therefore, the correct answer is **(B)

\frac{a n ^{2}}{V ^{2}}

**.

JEE Advanced · 2009 · 12 Apr 2009 · Paper 1 · Single correct option

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