An ideal gas is a scientific concept underpinning the Ideal Gas Law, of a theoretical gas with strictly defined properties for the purpose of understanding, predicting, and explaining the behavior of real gases under different conditions of temperature, pressure and volume. In an ideal gas:
- Molecules are spheres which collide elastically with each other and the container walls, so the total kinetic energy after a collision remains the same as before.
- There are no long-range forces of attraction or repulsion between molecules.
- Individual molecules occupy no volume, so a molecule’s size is ignored relative to the volume occupied by the gas as a whole.
In reality no real gas exhibits such properties without deviation, but most real gases at room temperature and normal atmospheric pressures behave sufficiently closely that the theoretical model is a useful approximation for scientific study.