AQA GCSE Gas Pressure and Volume

Gas Pressure

Gas pressure is caused by moving gas particles colliding with the walls of the container and exerting a force. This force exerted is gas pressure.

As the gas particle collides with the wall of the container a net force is exerted at 90 degrees to wall of the container.

Gas Pressure and Volume

There is a lot of space between the particles of a gas, so gases can be compressed.

When the plunger is pushed in the volume of the container will decrease, this will increase the pressure.

When the volume of the container is smaller, the gas particles collide with the walls of the container more frequently, so gas exerts a larger net force, so gas pressure increases.

Generally:

Pressure increases, as the gas is compressed in a smaller container

Pressure decreases as the gas expands in a larger container.

Boyles Law

Pressure and volume are inversely proportional to each other. This means that as Volume increases, pressure will decrease.

If there is a fixed mass of gas at constant temperature then:

Pressure,P x Volume,V = Constant

This equation can be rewritten as:

Pressure₁,P₁ x Volume₁,V₁ = Pressure₂,P₂ x Volume₂,V₂

P₁ xV₁ = P₂ x V₂

P₁ = Initial pressure (Pa)

P₂ = Final pressure (Pa)

V₁ = Initial volume (m³)

V₂ = Final volume (m³)

A gas has a volume of 100m³ and a pressure of 20Pa. It is compressed to occupy a volume of 40m³. Calculate the new pressure.

Initial pressure P₁ = 20Pa

Initial Volume V₁ = 100m³

Final volume V₂ = 40m³

Final pressure P₂ = ?

See the video below for workings and solution

Practice Questions

1. Explain how gas pressure is caused.

2. State the relationship between gas pressure and gas volume

3. Describe the appearance of a graph that has gas pressure on the Y axis and 1/volume on the X axis

4. Gas Y is compressed down to a volume of 20m3 with a gas pressure of 50Pa. The original gas has a pressure of 15Pa. Calculate the original gas volume before compression.