Edexcel IGCSE Chemistry

Revision Notes

1.5.10 Calculate Volumes of Gases

Calculate Volumes of Gases

Avogadro’s Law

  • Avogadro’s Law states that at the same conditions of temperature and pressure, equal amounts of gases occupy the same volume of space
  • At room temperature and pressure, the volume occupied by one mole of any gas was found to be 24 dm3 or 24,000 cm3
  • This is known as the molar gas volume at RTP
  • RTP stands for “room temperature and pressure” and the conditions are 20 ºC and 1 atmosphere (atm)
  • From the molar gas volume the following formula triangle can be derived:

Molar Volume dm3 (decimetre) Formula Triangle, IGCSE & GCSE Chemistry revision notes

Formula triangle showing the relationship between moles of gas, volume in dm3 and the molar volume

  • If the volume is given in cm3 instead of dm3, then divide by 24,000 instead of 24:

Molar Volume cm3 Formula Triangle, IGCSE & GCSE Chemistry revision notes

Formula triangle showing the relationship between moles of gas, volume in cmand the molar volume

  • The formula can be used to calculate the number of moles of gases from a given volume or vice versa
  • Simply cover the one you want and the triangle tells you what to do

To find the volume

Volume = Moles x Molar Volume

Examples of Converting Moles into Volumes Table

Examples of Converting Moles into Volumes Table, downloadable IGCSE & GCSE Chemistry revision notes

To find the moles

Moles = Volume ÷ Molar Volume

Examples of Converting Volumes into Moles Table

Examples of Converting Volumes into Moles Table, downloadable IGCSE & GCSE Chemistry revision notes

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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