GCSE Chemistry (AQA)

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Gas Volume Calculations

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

Gas Volume Calculations

6:59 Amount of Substance and Gas Volume
Spec 4.3.5
Previous Volumes of Gases Next Advanced Gas Volume Calculations
  • Every mole of any gas has the same volume under the same temperature and pressure.
  • This fact simplifies calculations involving gases.
  • The volume of gas reactants and products can be calculated from balanced symbol equations.
  • Example reaction: H2 + Cl2 ��� 2 HCl.
  • The balanced equation shows the ratio of moles and can be used to calculate gas volumes.
  • If 100 cm�� of hydrogen is used, the same volume of chlorine is used, and 200 cm�� of hydrogen chloride is produced.
  • This method works in reverse if the volume of a product is known.
  • Example problem: 50 cm�� of C2H6 reacts with 200 cm�� of O2.
  • Oxygen is in excess, so not all of it reacts.
  • The balanced equation: 2 C2H6 + 7 O2 ��� 4 CO2 + 6 H2O.
  • Mole ratio: 2:7:4:6.
  • Calculate the volume of O2 that reacts with C2H6: 50 cm�� x (7/2) = 175 cm��.
  • Remaining O2 volume: 200 cm�� - 175 cm�� = 25 cm��.
  • Calculate volumes of CO2 and H2O produced using the mole ratio.
  • CO2 volume: 50 cm�� x 2 = 100 cm��.
  • H2O volume: 50 cm�� x 3 = 150 cm��.
  • Total volume of gases after reaction: 25 + 100 + 150 = 275 cm��.

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