Fugacity

2013-12-09T05:26:12Z

129.15.139.155:

In [[thermodynamics]], the '''fugacity''' is a [[state function]] of any [[wikt:isothermal|isothermal]] system. The fugacity, which has units of [[pressure]], represents the [[wikt:tendency|tendency]] of a [[fluid]] to escape or expand [[wikt:isothermally|isothermally]]. For [[gas]]es at low pressures where the [[ideal gas law]] holds, fugacity is equal to pressure. The ratio <math> \phi = f/P \,</math> between fugacity <math>f\,</math> and pressure <math>P\,</math> is called the '''fugacity coefficient'''; therefore, <math> \phi = 1 \,</math> for an [[ideal gas]].

The fugacity <math> f\,</math> is defined at fixed [[temperature]] <math> T\,</math> by the following differential relation:

:<math> d \ln f = {dG \over RT} = {{V dP} \over RT} \,</math>

where <math>G\,</math> is the [[Gibbs free energy]], <math>R\,</math> is the molar gas constant, and <math>V\,</math> is the fluid's [[volume]]. For any two [[wikt:isothermal|isothermal]] physical states, represented by subscripts 1 and 2, the ratio of the two fugacities is as follows:

:<math> f_2 / f_1 = exp \left ({1 \over RT} \int_{G_1}^{G_2} dG \right) = exp \left ({1 \over RT} \int_{P_1}^{P_2} V\,dP \right) \,</math>

[[Category:Thermodynamics]]

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Fugacity