2 Enrichment: the ideal gas equation

In general, PV = nRT, where

• n = number of moles of the gas,
• P in pascals, V in m³, T in kelvin,
• R = 8.31 J/(mol·K) the universal gas constant. A mole is the amount of a substance whose mass in grams equals its molecular mass: one mole of oxygen (O₂) has a mass of 32 g; nitrogen (N₂) 28 g; carbon dioxide (CO₂) 44 g.

Example: the volume of one mole of any gas at STP is V = nRT/P = 1 × 8.31 × 273/1.013 × 10⁵ = 0.0224 m³ = 22.4 litres.