Boyle Law
At constant temperature, pressure and volume are inversely related.
Formula
Variables
Example
Squeeze a gas, pressure rises
How it works
Boyle’s law says that if the temperature and amount of gas stay the same, making a gas take up less space forces its pressure to increase, and letting it expand lowers the pressure. This happens because the gas particles keep colliding with the container walls; in a smaller volume, they hit the walls more often, so the pressure rises. The equation P1V1 = P2V2 lets you compare an initial and final state of the same gas under constant temperature.
When to use it
Use this law when a gas is compressed or expanded without changing temperature, such as in syringes, scuba gear, air pumps, or sealed gas containers. It is also useful for solving simple chemistry and physics problems involving changes in gas pressure and volume.
Worked example, step by step
A gas occupies 4.0 L at a pressure of 100 kPa. If the pressure is increased to 160 kPa at constant temperature, what is the new volume? P1V1 = P2V2 (100 kPa)(4.0 L) = (160 kPa)(V2) 400 kPa·L = 160 kPa·V2 V2 = 400 ÷ 160 V2 = 2.5 L Final answer: the gas volume decreases to 2.5 L.
Common mistakes to avoid
- Forgetting that temperature must stay constant for Boyle’s law to apply
- Mixing up which value is P1, V1, P2, and V2
- Using inconsistent units, such as litres for one volume and millilitres for the other without converting
Did You Know?
Boyle's law is why your ears pop on a plane: falling pressure lets trapped air expand.
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