What is the ideal gas law and when is it valid?

The ideal gas law states PV = nRT, where P is pressure, V is volume, n is moles, R is universal gas constant (8.314 J/mol-K), and T is absolute temperature. It assumes molecules have no volume and no intermolecular forces. Valid when: pressure is low (typically <5-10 bar), temperature is high (well above critical), and gas is not near condensation. Deviations are quantified by compressibility factor Z = PV/nRT; ideal gas has Z=1. Real gases deviate, requiring equations of state for accurate calculations.