# Ideal gas law

For a gas, PV = nRT, with pressure in pascals, volume in cubic metres and temperature in kelvin. R is 8.314 J/(mol K).

Physics (university) · Part 06: Thermodynamics · Card 6 of 10 · Last updated 2026-10-19

## Analogy

A balloon grows when warmed because the gas pushes harder.

## Example

**One mole of gas**

V = nRT / P
V = 8.314 x 273.15 / 101,325
V = 0.0224 m^3 = 22.4 L

## In practice

One mole at 273 K and 1 atm fills about 22.4 litres.

## Practice

### Flashcards

- **Write the ideal gas law.** PV = nRT.

## Questions people ask

### What makes a gas ideal?

An ideal gas has tiny particles that do not attract each other and collide perfectly elastically. Real gases such as air at room conditions act almost ideally. At very high pressure or low temperature, particle size and attraction matter, and the ideal gas law becomes less accurate.

### How do I use the ideal gas law with a changing gas?

For a fixed amount of gas, nR is constant, so P1V1/T1 equals P2V2/T2. Keep temperatures in kelvin. If you know three of the four values you can find the last one. This avoids needing the number of moles or the value of R.

## Related concepts

- [Temperature](https://studyvisually.com/learn/science/physics-university/physics-university-part-6/physics-university-part-6-concept-1)
- [Thermal expansion](https://studyvisually.com/learn/science/physics-university/physics-university-part-6/physics-university-part-6-concept-2)
- [Specific heat](https://studyvisually.com/learn/science/physics-university/physics-university-part-6/physics-university-part-6-concept-3)
- [Latent heat](https://studyvisually.com/learn/science/physics-university/physics-university-part-6/physics-university-part-6-concept-4)

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