Avogadros Law (Edexcel GCSE Chemistry): Revision Notes
📚 Revision Notes
Avogadros Law
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Avogadro's Law describes the relationship between the volume of a gas and the amount of gas particles (measured in moles) when temperature and pressure are kept constant.
- At the same temperature and pressure, equal volumes of any gas contain the same number of particles (atoms or molecules).
Why is Avogadro's Law Important?
Avogadro's Law helps chemists understand how gases behave under different conditions. It's particularly useful in:
- Calculating gas volumes in chemical reactions (especially reactions involving gases).
- Explaining the behaviour of gases in everyday life (like inflating balloons or car tyres).
The Law Explained:
The law can be written as:
Where:
- = volume of the gas
- = number of moles of the gas
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In simple terms:
- If you increase the number of gas particles (moles), the volume of the gas also increases, as long as the temperature and pressure stay the same.
- If you decrease the number of gas particles, the volume decreases.
For example:
- If you double the amount of gas (in moles), the volume of the gas will also double.
- If you halve the number of gas particles, the volume will halve.
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Mathematical Form of Avogadro's Law:
Where:
- and are the initial volume and number of moles
- and are the final volume and number of moles This equation helps you calculate how the volume of a gas changes when you add or remove moles.
Applications of Avogadro's Law:
-
Determining Gas Volumes: Avogadro's Law allows scientists to predict how the volume of a gas will change when more gas is added or removed, without changing the temperature or pressure.
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Standard Molar Volume: At standard temperature and pressure (STP), which is 0°C (273K) and 1 atmosphere pressure, 1 mole of any gas occupies 22.4 dm³ (this is called the molar volume of a gas at STP).
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Example:
- 1 mole of oxygen gas (O₂) at STP takes up 22.4 dm³.
- 2 moles of oxygen gas would take up 44.8 dm³.