States of Matter - Result Question 14

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

(2009)

(a) $n b$

(b) $n^{2} a / V^{2}$

(c) $-\left(n^{2} a / V^{2}\right)$

(d) $-n b$

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Answer:

Correct Answer: 14. (b)

Solution:

In the van der Waals’ equation

$ \left(p+\dfrac{n^{2} a}{V^{2}}\right)(V-n b)=n R T $

The additional factor in pressure, i.e. $\dfrac{n^{2} a}{V^{2}}$ corrects for intermolecular force while $b$ corrects for molecular volume.