Molar Volume
Chemistry: Cambridge International A Level, topic 1.1.6
Molar Calculations of Gases
We can also calculate the number of moles of a gas. It is difficult to measure the mass or the concentration of a gas so we must use another equation.
Avogadro's Law
- The equation is based upon Avogadro's Law:
- Avogadro's Law says that at the same temperature and pressure, one mole of two different gases will be the same volume.
- So, regardless of what the gas is, one mole of a gas will always be a particular volume at a specific temperature and pressure.
Room temperature and pressure
- At room temperature and pressure, 24 dm3 is the volume taken up by one mole of any gas.
The equation for moles in a gas
- This leads to the equation:
- Number of moles of a gas = volume of the gas ÷ 24
- This equation is only true if:
- The volume is measured in dm3.
- The gas is at room temperature and pressure.
The equation for volume of a gas
- Another form of this equation gives the equation
- Volume of a gas = moles of the gas × 24
- This equation volume calculated:
- Is in dm3.
- Is correct at room temperature and pressure.
Converting the equation
- A useful conversion for this equation is:
- 1 m3 = 1,000 dm3
- Alternatively, we can use the converted equation:
- Number of moles of a gas = volume of the gas ÷ 24,000
- Volume of a gas = number of moles of the gas × 24,000
- This is true for the volume in cm3.
Test yourself on Molar Volume
At room temperature and pressure, what volume is taken up by one mole of a gas?
How do we calculate the number of moles of a gas at room temperature and pressure?
What is the equation for the volume of a gas at room temperature and pressure?