An ideal gas is a theoretical concept assuming gas particles have no volume and no attractive forces between them. Real gases have particle volume and intermolecular forces, deviating from ideal behavior, especially at high pressures and low temperatures.

An ideal gas follows the ideal gas law (PV=nRT) under all conditions, assuming no intermolecular forces and negligible molecular volume. In contrast, real gases deviate from this behaviour at low temperatures and high pressures due to intermolecular attractions and the finite volume of molecules.