Question

A chamber contains monoatomic ${}^{\prime }H{e}^{\prime }$ at STP, determine its number density.

Answer 1

Number density $=\frac{P}{kT}$
(where, $k=$ Boltzmann constant)
$PV=nRT$
$=(n\times N)\frac{R}{N}T$
$=(n\times N)kT$
$\frac{P}{kT}=\frac{n\times N}{V}=$ number density
$\therefore$ Number density $=\frac{1.01\times {10}^5}{1.38\times {10}^{-23}\times 273}=2.68\times {10}^{25}{m}^{-3}$.