Calculate Volumes of Gases (Edexcel IGCSE Chemistry)
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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:
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:
Formula triangle showing the relationship between moles of gas, volume in cm3 and 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
Name of Gas | Amount of Gas | Volume of Gas |
Hydrogen | 3 mol | (3 x 24) = 72 dm3 |
Carbon Dioxide | 0.25 mol | (0.25 x 24) = 6 dm3 |
Oxygen | 5.4 mol | (5.4 x 24,000) = 129,600 cm3 |
Ammonia | 0.02 mol | (0.02 x 24) = 0.48 dm3 |
To find the moles
Moles = Volume ÷ Molar Volume
Examples of Converting Volumes into Moles Table
Name of Gas | Volume of Gas | Amount of Gas |
Methane | 225.6 dm3 | (225.6 ÷ 24) = 9.4 mol |
Carbon Monoxide | 7.2 dm3 | (7.2 ÷ 24) = 0.3 mol |
Sulfur Dioxide | 960 dm3 | (960 ÷ 24) = 40 mol |
Oxygen | 1200 cm3 | (1200 ÷ 24,000) = 0.05 mol |
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