Fugacity


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fugacity

[fyü′gas·əd·ē]
(thermodynamics)
A function used as an analog of the partial pressure in applying thermodynamics to real systems; at a constant temperature it is proportional to the exponential of the ratio of the chemical potential of a constituent of a system divided by the product of the gas constant and the temperature, and it approaches the partial pressure as the total pressure of the gas approaches zero.

Fugacity

 

a quantity used to calculate the properties of real gases by means of the thermodynamic relationships developed for ideal gases (seeGASES). The concept of fugacity was introduced by G. Lewis in 1901.

The fugacity f of a given gas or a given component of a gas mixture is a function of pressure p and temperature T and of the concentration of each component of a mixture. When the fugacity is substituted for the partial pressure in the thermodynamic equations for an ideal gas, the equations are rendered valid for a real gas under the conditions considered. Although this technique is a formal mathematical procedure, it is productive because the use of more complex equations of state for real gases entails substantial computational difficulties and may not provide the necessary accuracy, since any equation of state for a real gas is valid only within a specific range of values of p and T.

The ratio flp is called the fugacity coefficient; for an ideal gas, it is obviously equal to unity under any conditions. Thus, the difference between the value of flp and unity characterizes the extent to which a gas departs from the ideal state. The role of the fugacity of a gas with respect to the partial pressure of the gas is similar to the role of the activity of a component of a solution with respect to the concentration of the component.

Since the fugacity of a substance that forms or is a constituent of a condensed phase is equal to the fugacity of the substance in the saturated vapor of the phase, the fugacity may also be regarded as a value that quantitatively characterizes—for a given p, T, and phase composition—the ability of the substance to leave the phase.

REFERENCES

See references under THERMODYNAMICS, CHEMICAL.

M. KH. KARAPET’IANTS

References in periodicals archive ?
They considered moderate and high pressure levels, and reported activity and fugacity coefficients of each component in the mixtures through Lewis rule and Redlich-Kwong state equation for carbon dioxide in vapor phase.
where [x.sub.gas] is the mole fraction of dissolved gas in the condensed phase (which will be zero for ice and can be computed from Henry's law for gases in liquid water at low and moderate pressures), [[phi].sub.vap.sub.w] is the fugacity coefficient of water in the equilibrium vapor, and y is the vector of mole fractions representing the equilibrium composition of the vapor phase.
Mackay, D., Multimedia Environmental Models: The Fugacity Approach, 2a edicion, 1-261.
145 (1751), Johnson moves from a focus on fugitive texts themselves and on fugacity in general to the writers who produce such texts, introducing authorship rather than the form of the book miscellany or repository as a means of mediating ephemerality.
The critical fugacity for surface adsorption of self-avoiding walks on the honeycomb lattice is 1 + %/2.
The central action of Canto XXIV is the instantaneous reduction to ashes, in order to be restored and start over again, like the phoenix, of Vanni Fucci, whose very name rings with vain fugacity (vanitas) and the fact that he was here (ci fu).
Modelling of pharmaceutical residues in Australian sewage by quantities of use and fugacity calculations.
In the unsecured labyrinths of nihilism that imprison us in the vertigo of time reduced to the momentum, the death of God threatens to clone and replicate itself in the human subject, whose life becomes an inert function and instrument within the mere scope of the activities that man creates to which he offers wholly himself confined in the fugacity and voracity of the present moment.
We have predicted conditions (pressure, temperature, oxygen fugacity) necessary for stability of these new materials, and some planets, though probably not the Earth, may offer such conditions," added Oganov.
Tellez, "Equation of state in the fugacity format for the two-dimensional Coulomb gas", J.
All calculations are performed within an approximation of the use of concentration rather than thermodynamic activity or fugacity, but that usage, despite its prospectively severe inaccuracy, is standard practice in general chemistry; the additional complications of activity coefficients are typically left to advanced courses in analytical and physical chemistry.
xC[O.sub.2] was converted into pC[O.sub.2] and the fugacity of C[O.sub.2] (fC[O.sub.2]) according to equations provided by Zeebe and Wolf-Gladrow (2001).