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An ideal gas sample has volume V, pressure P, and absolute temperature T. If the mass of one molecule is m, which expression gives the density of the gas?

1. mkT
2. P/kT
3. P/(kT V)
4. Pm/kT

Correct answer: Pm/kT

Solution

From PV = NkT, number of molecules N = PV/(kT). Mass = N*m = PVm/(kT), so density = mass/V = Pm/(kT).

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