“m” is the mass of a molecule, “k” is the Boltzmann constant, P is the pressure and T is the absolute temperature. The density of the gas is given by

Density Formula for a Gas

The density (ρ) of a gas is expressed in terms of the mass of a molecule (m), Boltzmann constant (k), pressure (P), and temperature (T) as:

ρ = mP / kT

• m: mass of a molecule
• P: pressure
• k: Boltzmann constant
• T: absolute temperature

Derivation: From the ideal gas law, PV = NkT, we get N/V = P/kT. Since density is mass per unit volume and equals ρ = (Nm)/V, we substitute N/V to get ρ = mP / kT.