How It Works: Why 1 Mole of Any Gas = 24 dm³

⚙️ How It Works: Why 1 Mole of Any Gas = 24 dm³

In a gas, the particles are very far apart from each other — the space between particles is much larger than the particles themselves. This means the volume of a gas is determined almost entirely by how many particles there are and how energetically they are moving, not by the size or mass of the individual particles.

At a given temperature (which determines how fast particles move) and a given pressure (which determines how hard they push on the container walls), the volume depends only on the number of particles. Since one mole always contains the same number of particles (Avogadro's constant, 6.02 × 10²³), one mole of any gas at the same temperature and pressure will occupy the same volume.

At RTP (Room Temperature and Pressure, defined as 20°C and 1 atmosphere), this volume is 24 dm³ (24,000 cm³). This is different from STP (standard temperature and pressure, 0°C and 1 atm) where the molar volume is 22.4 dm³ — GCSE uses the RTP value of 24 dm³.

The practical consequence is elegant: to find the volume of a gas from a reaction, you simply: (1) find the moles of gas from the balanced equation, then (2) multiply by 24. No complicated density calculations needed.