Theorem of Corresponding States

The theorem of corresponding states says that substances at equal reduced temperature and pressure exhibit approximately similar thermodynamic behavior, largely independent of chemical identity.

Reduced temperature: A temperature expressed as a ratio to a substance’s critical temperature. It lets different substances be compared at the same fraction of their critical temperatures.
Equation of state: A mathematical relation among the state variables of a physical system. Corresponding states compares the equations of state of different substances.
Generalized compressibility chart: A chart estimating gas compressibility from reduced pressure and reduced temperature. It applies corresponding-states behavior to estimate real-gas properties.
Ideal gas law: An equation relating pressure, volume, temperature, and amount for an idealized gas with negligible molecular interactions. It describes the dilute limit, while corresponding states addresses nonideal fluid behavior too.
Reduced pressure: A pressure expressed as a ratio to a substance’s critical pressure. It supplies the pressure coordinate for corresponding-states comparisons.
Critical temperature: The highest temperature at which a substance can exist as a liquid. It is the reference temperature in the reduced-temperature definition.
Pitzer correlations: Empirical fluid-property correlations that account for acentric-factor departures from simple-fluid behavior. They improve corresponding-states estimates using a substance-specific correction.
Principle of corresponding states: A broad physical idea that systems with suitably scaled variables can exhibit similar behavior. This wider principle spans fields, whereas the theorem concerns fluid thermodynamics.
Critical point: The state at which liquid and gas phases become indistinguishable. Its temperature and pressure define the scales used to reduce fluid properties.
Critical pressure: The pressure at a substance’s critical point. It is the reference pressure in the reduced-pressure definition.

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