In chemical thermodynamics, the fugacity of a real gas is an effective partial pressure which replaces the mechanical partial pressure in an accurate computation of chemical equilibrium. It is equal to the pressure of an ideal gas which has the same temperature and molar Gibbs free energy as the real gas.[1]
Fugacities are determined experimentally or estimated from various models such as a Van der Waals gas that are closer to reality than an ideal gas. The real gas pressure and fugacity are related through the dimensionless fugacity coefficient[1]
For an ideal gas, fugacity and pressure are equal, and so φ = 1. Taken at the same temperature and pressure, the difference between the molar Gibbs free energies of a real gas and the corresponding ideal gas is equal to RT ln φ.
The fugacity is closely related to the thermodynamic activity. For a gas, the activity is simply the fugacity divided by a reference pressure to give a dimensionless quantity. This reference pressure is called the standard state and normally chosen as 1 atmosphere or 1 bar.
Accurate calculations of chemical equilibrium for real gases should use the fugacity rather than the pressure. The thermodynamic condition for chemical equilibrium is that the total chemical potential of reactants is equal to that of products. If the chemical potential of each gas is expressed as a function of fugacity, the equilibrium condition may be transformed into the familiar reaction quotient form (or law of mass action) except that the pressures are replaced by fugacities.
For a condensed phase (liquid or solid) in equilibrium with its vapor phase, the chemical potential is equal to that of the vapor, and therefore the fugacity is equal to the fugacity of the vapor. This fugacity is approximately equal to the vapor pressure when the vapor pressure is not too high.
^ abAtkins, Peter; De Paula, Julio (2006). Atkins' Physical Chemistry (8th ed.). W. H. Freeman. pp. 111–2. ISBN 9780716787594.
and fugacity are related through the dimensionless fugacity coefficient φ = f P . {\displaystyle \varphi ={\frac {f}{P}}.} For an ideal gas, fugacity and...
how to utilize the fugacity capacity to calculate the concentration of a chemical in a system. Depending on the chemical, fugacity capacity varies. The...
well as from mathematical models. One of these mathematical models is a fugacity-based BCF model developed by Don Mackay. Bioconcentration factor can also...
deviates from the ideal case. The compressibility factor is linked to the fugacity by the relation:[citation needed] f = P exp ( ∫ Z − 1 P d P ) {\displaystyle...
a redox buffer, then the oxygen fugacity of equilibration is defined by one of the curves in the accompanying fugacity-temperature diagram. Redox buffers...
question that includes fugacities, concentrations, fluxes and amounts. The important values are the proportionality constant, called fugacity capacity expressed...
gas i is given by its fugacity fi: this may be higher or lower than its mechanical pressure. By historical convention, fugacities have the dimension of...
as the oxygen fugacity ( f O 2 {\displaystyle fO_{2}} ) of the system within the framework of thermodynamics. A higher oxygen fugacity implies a more...
temperature of equilibrium between ore and water, determine pH and oxygen fugacity, identify the activity of sulfate-reducing bacteria in the time of formation...
reaction is used to control the fugacity of oxygen in laboratory experiments. It can also be used to calculate the fugacity of oxygen recorded by mineral...
obeys the fugacity analogue of Raoult's law f i = x i f i ∗ {\displaystyle f_{i}=x_{i}f_{i}^{*}} . Here f i {\displaystyle f_{i}} is the fugacity of component...
a buffer that can control how oxidizing its environment is (the oxygen fugacity). This buffer is known as the hematite-magnetite or HM buffer. At lower...
entropy of a gas is proportional to its pressure (or, more precisely, to its fugacity): the entropies of liquids vary little with pressure, as the compressibility...
coexisting carbonates and sulfides can be used to determine the pH and oxygen fugacity of the ore-bearing fluid during ore formation. In most forest ecosystems...
different buffers. For equilibria in a gas phase, fugacity, f, is used in place of activity. However, fugacity has the dimension of pressure, so it must be...
activity of gaseous hydrogen (H 2), which is approximated here by its fugacity p H 2 . {\displaystyle p_{\mathrm {H_{2}} }.} p H 2 {\displaystyle p_{\mathrm...
is extremely rare and can only be found as a minor phase in low oxygen fugacity environments, such as the interiors of certain volcanoes. Native aluminium...
concentration and fugacity coefficient in place of activity coefficient. In the real world, for example, when making ammonia in industry, fugacity coefficients...
representation for an aromatic functional group in organic chemistry. The fugacity coefficient in thermodynamics. The ratio of free energy destabilizations...
(2004). "An experimental investigation of the influence of water and oxygen fugacity on differentiation of MORB at 200 MPa". Journal of Petrology. 46 (1): 135–167...
pressure of mixtures of liquids. It states that the activity (pressure or fugacity) of a single-phase mixture is equal to the mole-fraction-weighted sum of...
(May 1986). "The color of meteoritic hibonite: an indicator of oxygen fugacity". Earth and Planetary Science Letters. 78 (1): 67–79. Bibcode:1986E&PSL...
descend into the mantle before being stabilised at depth by low oxygen fugacity environments. Magnesium, iron, and other metallic compounds act as buffers...
{G}{N}}=\mu =\mu ^{\circ }+kT\ln {\frac {p}{p^{\circ }}}.} In non-ideal systems, fugacity comes into play. The Gibbs free energy total differential with respect...
contact with carbon-rich sedimentary rocks, which have reduced the oxygen fugacity sufficiently for iron to crystallize. This is known as telluric iron and...
Al)(SiO4)(Si2O7)O(OH). The presence of iron as Fe3+ and Fe2+ helps buffer oxygen fugacity, which in turn is a significant factor in petrogenesis. Other examples...
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