Ideal Gas Law — FAQ
Frequently asked questions about Ideal Gas Law (PV=nRT).
Q1. Why is temperature in Kelvin, not Celsius?
The ideal gas law requires absolute temperature. Kelvin starts at absolute zero (−273.15°C), where molecular motion ceases. Using Celsius would give wrong (or negative) results.
Q2. What is an 'ideal' gas?
An ideal gas assumes molecules have no volume and no intermolecular forces. Real gases deviate at high pressure and low temperature, but PV=nRT is an excellent approximation for most everyday conditions.
Q3. Where is the ideal gas law used in practice?
HVAC engineers calculate air volumes, divers compute gas consumption at depth, meteorologists model atmosphere layers, and engine designers optimise combustion chamber pressure.
Have more questions? Try the interactive calculator at /tools/ideal-gas-law-visualizer