GCSE Chemistry (AQA)

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Volumes of Gases

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Quantitative chemistry Use of amount of substance in relation to volumes of gases

Volumes of Gases

7:24 Amount of Substance and Gas Volume
Spec 4.3.5
Previous Calculating Concentration of a Reacting Solution Next Gas Volume Calculations
  • The volume of a gas varies with temperature and pressure.
  • Increasing temperature increases the volume of gas.
  • Gas molecules move faster at higher temperatures.
  • Increasing pressure decreases the volume of gas.
  • Gas molecules are forced together under higher pressure.
  • The volume of gas also depends on the number of moles.
  • Equal amounts in moles of gases occupy the same volume under the same conditions of temperature and pressure.
  • This principle holds true regardless of the gas identity.
  • Example: One mole of hydrogen (H2) and one mole of carbon dioxide (CO2) occupy the same volume under standard conditions.
  • At room temperature (20��C) and pressure (1 atmosphere), one mole of any gas occupies 24 dm��.
  • This volume is referred to as the molar volume.
  • Volume of gas at room temperature and pressure can be calculated using the equation: Volume (dm��) = Number of moles (N) �� 24 dm��.
  • Example calculation: 5 moles of gas at room temperature and pressure occupy 120 dm��.
  • To calculate the volume of 0.4 moles of C2H6 gas: Volume = 0.4 �� 24 = 9.6 dm��.
  • Volume of gas can also be calculated from its mass by first converting mass to moles using the equation: N = Mass (M) / Relative formula mass (Mr).
  • Example calculation: Find the volume of 0.66 grams of CO2 gas.
  • Step 1: Calculate moles: N = 0.66 / 44 = 0.015 moles.
  • Step 2: Calculate volume: Volume = 0.015 �� 24 = 0.36 dm��.

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