{"id":451,"date":"2026-07-09T12:00:37","date_gmt":"2026-07-09T12:00:37","guid":{"rendered":"https:\/\/physicsfundamentalsinfo.com\/blog\/?p=451"},"modified":"2026-07-09T12:00:38","modified_gmt":"2026-07-09T12:00:38","slug":"ideal-gas-law","status":"publish","type":"post","link":"https:\/\/physicsfundamentalsinfo.com\/blog\/thermodynamics\/ideal-gas-law\/","title":{"rendered":"What Is the Ideal Gas Law (PV = nRT)?"},"content":{"rendered":"\n
Definition<\/div>

\nThe ideal gas law states that the pressure of a gas multiplied by its volume equals the number of moles times the universal gas constant times the absolute temperature: PV = nRT. It ties four state variables together, so fixing any three fixes the fourth. Temperature must always be in kelvin, and pressure must be absolute.\n<\/p><\/div>\n

Leave a bag of crisps in a car on a hot afternoon and it comes back looking ready to burst. Nothing was added. No one pumped it up. The sealed air inside simply got hotter, and hotter air pushes harder.<\/p>\n

That puffed-up bag is the ideal gas law doing its work in a car park. The same equation sizes the airbag in your steering column, lifts a weather balloon fifteen times its ground volume, and tells a diver why holding your breath on the way up is the one thing you must never do.<\/p>\n

What Is the Ideal Gas Law?<\/h2>\n

Picture a gas as a swarm of molecules rattling around inside a container. You cannot track any single one of them. But you can measure four things about the swarm as a whole: how hard it pushes (pressure), how much room it has (volume), how many molecules there are (moles), and how fast they are moving on average (temperature).<\/p>\n

The ideal gas law is the statement that these four numbers are not independent. Lock three of them down and the fourth has no choice.<\/p>\n

That is a remarkable claim. It means you do not need to know what the gas is<\/em> \u2014 helium, nitrogen, carbon dioxide, the air in your lungs. At everyday pressures and temperatures they all obey the same equation, to within a percent or two.<\/p>\n

An ideal gas<\/strong> is the idealisation that makes this work: molecules with no volume of their own, which do not attract one another, and which bounce off the walls and each other without losing energy. Real gases are not quite that. They are close enough that the law runs almost every calculation in engineering thermodynamics.<\/p>\n

The Ideal Gas Law Formula: What Every Symbol Means<\/h2>\n
PV = nRT<\/div>\n

Each symbol carries a unit, and the units are where marks are lost. Here is the SI set:<\/p>\n