Boyle's Law
At constant temperature, P and V are inversely proportional.
About this topic
Boyle's law states that at constant temperature, the pressure of a fixed amount of gas is inversely proportional to its volume: P1V1 = P2V2. Squeezing a gas into half the volume doubles its pressure because particles hit the walls twice as often.
A graph of pressure against volume is a curve (hyperbola), and a graph of pressure against 1/V is a straight line. Robert Boyle found the relationship in 1662 by trapping air in a J-shaped tube of mercury. The key conditions are constant temperature and constant number of moles. Pressure and volume units only need to match on both sides.
Worked example: a 2.0 L balloon at 1.0 atm sinks to a depth where the pressure is 3.0 atm. Then V2 = (1.0 x 2.0) / 3.0 = 0.67 L. Scuba divers learn never to hold their breath when ascending because the air in their lungs would expand and could rupture tissue. Syringes, bicycle pumps and breathing all depend on this law: expanding the chest increases the volume, lowering pressure so that air flows in.
A common error is to think that pressure and volume are directly proportional. Another is using Celsius or mixed units. Remember that if the volume goes up, the pressure goes down.
Key ideas
- P₁V₁ = P₂V₂
- Squeeze a syringe: pressure rises
- Hyperbolic graph
Quick check
Use cases: where Boyle's Law helps
- Homework: review the key idea behind Boyle's Law before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Boyle's Law without notes.
- Visual learning: play with the interactive lab to see how Boyle's Law changes when you adjust its inputs.
- Teaching a friend: explain Boyle's Law in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Boyle's Law?
At constant temperature, P and V are inversely proportional.
What will I learn in Boyle's Law?
P₁V₁ = P₂V₂. Squeeze a syringe: pressure rises. Hyperbolic graph.
Is Boyle's Law part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Boyle's Law lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Boyle's Law?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.