One Number for Every Gas
📖 One Number for Every Gas
Think of gas particles as bouncing balls in a balloon. At room conditions, what matters isn't the SIZE of the balls, but how many there are and how fast they bounce. Since one mole always means the same NUMBER of particles (6.02 × 10²³), and they're all bouncing at the same speed (same temperature), they take up the same space — 24 dm³. Simple!
Why is this true? At the molecular level, gas particles are so far apart that their actual size doesn't matter — what matters is how many particles there are and how fast they're moving. Since temperature and pressure control this, and since a mole always means the same NUMBER of particles (6.02 × 10²³), one mole of any gas takes up the same space.
The molar gas volume at RTP (room temperature and pressure — 20°C and 1 atmosphere) is 24 dm³/mol or equivalently 24,000 cm³/mol.
This gives us a beautifully simple equation:
or
Moles = Volume (dm³) ÷ 24
Chemistry glossary
- What is the molar gas volume at RTP?
- 24 dm³/mol (or 24,000 cm³/mol) One mole of ANY gas occupies 24 dm³ at room temperature and pressure
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.
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🧠 Memory Aids
"24 is the magic number at RTP" — one mole of any gas = 24 dm³. Think of it as "two dozen" — 24 dm³, just like 24 hours in a day or 24 items in two dozen.
The gas triangle: Draw a triangle with Volume (V) at the top, Moles (n) bottom-left, and 24 bottom-right. Cover V → n × 24. Cover n → V ÷ 24. This is the gas equivalent of the moles triangle.
Unit check mantra: "cm³? Divide by 1000 to get dm³ FIRST." Always convert before using V = n × 24.
Multi-step route: "mass → moles → ratio → moles of gas → volume" — always follow this sequence for complex questions.
Now try it yourself
Quiz · Question 1 of 20
What is the molar gas volume at RTP (room temperature and pressure)?
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