Q. The pressure of 2 moles of ammonia at $27{^\circ}$ when its volume is 5 L according to van der Waals’ equation is (Given, $a = 4.17,\ b = 0.3711$)
A) 10.33 atm
B) 9.33 atm
C) 9.74 atm
D) 9.2 atm
Explanation
(b)
$\left( p + \frac{n^{2}a}{V^{2}} \right)(V - nb) = nRT$
$p = \frac{nRT}{(V - nb)} - \frac{an^{2}}{V^{2}}$
$= \frac{2 \times 0.082 \times 300}{5 - 2 \times 0.03711} - \frac{4.17 \times 4}{25}$
$= 9.33\ atm$
$\frac{U_{av}}{U_{rms}} = \sqrt{\frac{8RT}{\pi M} \times \frac{M}{3RT}}$
$= \sqrt{\frac{8}{3 \times \pi}}$
$= \sqrt{\frac{8}{3 \times 3.14}}$
$U_{av} = U_{rms} \times 0.9213$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.