A level Chemistry · Edexcel 9CH0 · Topic 5C
Gas volumes
Key points
- Avogadro's law: equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
- Molar volume at room temperature and pressure is 24.0 dm³ mol⁻¹ (24 000 cm³), so .
- Reacting gas volumes are in the same ratio as the moles in the balanced equation.
- Ideal gas equation: with in Pa, in m³, in K and = 8.31 J mol⁻¹ K⁻¹.
- Conversions: 1 dm³ = 10⁻³ m³; 1 cm³ = 10⁻⁶ m³; kPa × 1000 = Pa; °C + 273 = K.
- You can rearrange to find the molar mass of a volatile liquid: .
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Gases are hard to weigh but easy to measure by volume. Because equal volumes of different gases contain the same number of molecules, a gas volume tells you the amount in moles directly, and the ideal gas equation extends this to any…
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