10.03.09 Moles of Gas (HT)

Syllabus

Equal amounts in moles of gases occupy the same volume under the same conditions of temperature and pressure.
The volume of one mole of any gas at room temperature and pressure (20^oC and 1 atmosphere pressure) is 24 dm³ .
The volumes of gaseous reactants and products can be calculated from the balanced equation for the reaction.
Students should be able to:

calculate the volume of a gas at room temperature and pressure from its mass and relative formula mass
calculate volumes of gaseous reactants and products from a balanced equation and a given volume of a gaseous reactant or product.

What does this mean?

What is the Molar Gas Constant?

Gas particles are very small compared to the space between them.

So gases with slightly larger molecules don't actually occupy any additional space than gases with smaller molecules.

And this means that 1 mole of any gas always occupies the same space.

This is called the Molar Gas Volume.

And at Room Temperature and Pressure this volume is 24,000 cm³ or 24 dm³ (24 Litres)

Obviously particles occupy some space. Just not enough to be worth considering.

Finding the volume of a known number of moles.

The Molar Gas Constant means that if we know how many moles of gas there are, we know how much space it will occupy and we don't have to worry about which gas it is.

So, how much space would 3 moles of Oxygen occupy?

1 mole occupies 24,000 cm³ so 3 moles will occupy 3 x 24,000 cm³ = 72,000 cm³

So, how much space would 3 moles of Steam occupy?

1 mole occupies 24,000 cm³ so 3 moles will occupy 3 x 24,000 cm³ = 72,000 cm³