Ideal Gas Law
PV = nRT links pressure, volume, temperature and amount of gas.
About this topic
The ideal gas law PV = nRT links the pressure, volume, temperature (in kelvin) and amount of gas in moles, with R = 8.31 J/mol·K. Special cases: Boyle's law (P ∝ 1/V at constant T), Charles's law (V ∝ T at constant P) and Gay-Lussac's law (P ∝ T at constant V).
Real gases deviate at high pressure and low temperature, when molecules take up significant space and attract one another, but the law works well for air at everyday conditions. One mole of any ideal gas takes up about 22.4 litres at 0 °C and 1 atm. The law can be written PV = NkT using the number of molecules N.
Worked example: a tyre holds air at 200 kPa and 15 °C (288 K). After a long drive it warms to 45 °C (318 K) at fixed volume, so P = 200 × 318 / 288 ≈ 221 kPa, which is why you check tyre pressure when cold. A sealed balloon taken into a freezer shrinks as the temperature falls.
Applications include scuba tanks, weather balloons, engines and syringes. The most common mistake is using Celsius instead of kelvin. Another is forgetting that pressure in the law must be absolute, not gauge pressure. Check that units match R before calculating.
Key ideas
- Boyle: P ∝ 1/V at constant T
- Charles: V ∝ T at constant P
- Use kelvin
Quick check
Use cases: where Ideal Gas Law helps
- Homework: review the key idea behind Ideal Gas Law before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Ideal Gas Law without notes.
- Visual learning: play with the interactive lab to see how Ideal Gas Law changes when you adjust its inputs.
- Teaching a friend: explain Ideal Gas Law in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Ideal Gas Law?
PV = nRT links pressure, volume, temperature and amount of gas.
What will I learn in Ideal Gas Law?
Boyle: P ∝ 1/V at constant T. Charles: V ∝ T at constant P. Use kelvin.
Is Ideal Gas Law part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Ideal Gas 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 Ideal Gas 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.