## College Physics (4th Edition)

We can find an expression for the number density $\frac{N}{V}$: $PV = NkT$ $\frac{N}{V} = \frac{P}{kT}$ Since the volume, pressure, and temperature are equal for both gases, the number density for each gas is equal. However, since each nitrogen particle has a higher mass than each helium particle, nitrogen has a higher mass density.