Vapour density

Vapour density is the density of a vapour in relation to that of hydrogen. It may be defined as mass of a certain volume of a substance divided by mass of same volume of hydrogen.

vapour density = mass of n molecules of gas / mass of n molecules of hydrogen gas .

vapour density = molar mass of gas / molar mass of H₂

vapour density = molar mass of gas / 2.01568

vapour density = 1⁄2 × molar mass

(and thus: molar mass = ~2 × vapour density) For example, vapour density of mixture of NO₂ and N₂O₄ is 38.3. Vapour density is a dimensionless quantity.

Vapour density = density of gas / density of hydrogen (H2)