Knowra Fugacity Fugacity Fugacity is a thermodynamic quantity that replaces pressure in chemical-potential and chemical-equilibrium calculations for nonideal substances. It equals pressure in the ideal-gas limit.
Fugacity coefficient : The ratio of a substance’s fugacity to its pressure, measuring deviation from ideal-gas behavior. It converts pressure into fugacity for real gases.
Chemical equilibrium : A state in which forward and reverse chemical reactions proceed at equal rates, leaving composition macroscopically constant. Equilibrium constants are formulated using activities, which incorporate fugacity for gases.
Thermodynamic activity : A dimensionless measure of a component’s effective concentration relative to a chosen standard state. Fugacity is the gas-phase quantity used to construct thermodynamic activity.
Gilbert N. Lewis : An American physical chemist whose work shaped chemical thermodynamics and introduced the concept of fugacity. Lewis introduced fugacity as an effective pressure for real substances.
Equation of state : A relation connecting the pressure, volume, temperature, and composition of a thermodynamic system. Equations of state provide routes to calculate fugacity from real-fluid properties.
Phase equilibrium : A state in which coexisting phases have equal temperature, pressure, and chemical potential for each component. Equality of fugacity across phases supplies the chemical-potential condition for equilibrium.
Ideal gas : A model gas whose particles have negligible volume and intermolecular interactions. For an ideal gas, fugacity equals pressure exactly.
Thermodynamic potential : A state function, such as Gibbs free energy, used to characterize a system and predict its equilibrium behavior. Fugacity emerged from expressing real-fluid chemical potentials in a pressure-like form.
Partial pressure : The pressure a gas component would exert if it alone occupied the mixture’s volume at the same temperature. Partial pressure approximates fugacity for ideal mixtures but misses nonideal interactions.
Vapor–liquid equilibrium : The equilibrium distribution of components between vapor and liquid phases in a mixture. Fugacity balances connect vapor and liquid compositions when either phase is nonideal.
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