# 2.1.5 Pressure Changes

### Pressure & Temperature

• The molecules in a gas move around randomly at high speeds, colliding with surfaces and exerting pressure upon them

Gas molecules collide with surfaces, exerting pressure

• When the temperature of a gas is increased, the speeds of the molecules increases
• This causes them to collide harder against surfaces, increasing the pressure
• Increasing the temperature of a gas (whilst keeping its volume fixed) will increase the pressure

### Pressure & Volume

• When a gas is compressed, the density of the gas increases

When a gas is compressed it becomes more dense, increasing the pressure

• This means there will be more collisions against surfaces, which will also increase the pressure
• Decreasing the volume of a gas (whilst keeping the temperature fixed) will increase the pressure

Worked example showing the effect of compressing gas on its pressure

Extended Only

### Boyle's Law

• If a gas has an original pressure, P1, and volume, V1, then its final pressure and volume (P2 and V2) will be given by the relationship:
`P1V1 = P2V2`

Note: The above equation only works if the temperature of the gas remains constant

Worked example showing the change in pressure of gas as the result of compression

### Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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