Real gas

A real gas consists of molecules with finite size and intermolecular forces. These features cause its behavior to depart from the ideal gas law, especially at high pressure or low temperature.

Van der Waals equation: An equation of state that corrects the ideal gas law for molecular size and intermolecular attraction. Its two correction terms model the finite volume and attractive forces that make gases real.
Ideal gas: A theoretical gas whose particles have negligible volume and no intermolecular forces. It supplies the limiting model that real gases depart from.
Gas liquefaction: The conversion of a gas into a liquid by cooling, compression, or both. Real-gas attractions make liquefaction possible below a critical temperature.
Ideal gas law: The relation PV = nRT connecting pressure, volume, amount, and temperature for an ideal gas. It predicts real-gas behavior accurately only when nonideal effects are small.
Compressibility factor: A dimensionless ratio comparing a gas’s measured molar volume with the ideal-gas prediction. It quantifies how far a real gas departs from ideal behavior.
Kinetic theory of gases: A molecular model that explains gas pressure and temperature through particle motion and collisions. Its ideal assumptions make the source of real-gas corrections explicit.
Peng–Robinson equation of state: A cubic equation of state used to estimate fluid properties, especially in chemical engineering. It predicts real-fluid phase behavior for process design.
Boyle’s law: The inverse relationship between pressure and volume for a fixed amount of gas at constant temperature. Real gases depart from this relationship as compression strengthens molecular effects.
Virial equation of state: A series expansion expressing a gas’s compressibility factor in powers of inverse molar volume. Its coefficients encode molecular interactions underlying nonideal behavior.
Equation of state: A mathematical relation connecting thermodynamic properties such as pressure, volume, and temperature. Real-gas equations refine this general description of matter.

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