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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク fugacity ： ウィキペディア英語版 fugacity In chemical thermodynamics, the fugacity ($f$) of a real gas is an effective pressure which replaces the true mechanical pressure in accurate chemical equilibrium calculations. It is equal to the pressure of an ideal gas which has the same chemical potential as the real gas. For example, nitrogen gas (N2) at 0°C and a pressure of $P=100\backslash ,\backslash rm\; atm$ has a fugacity of $f=97.03\backslash ,\backslash rm\; atm$.〔Peter Atkins and Julio de Paula, ''Atkins' Physical Chemistry'' (8th edn, W.H. Freeman 2006), p.112〕 This means that the chemical potential of real nitrogen at a pressure of 100 atm is less than if nitrogen were an ideal gas; the value of the chemical potential is that which nitrogen as an ideal gas would have at a pressure of 97.03 atm 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 ideal gas pressure and fugacity are related through the dimensionless fugacity coefficient $\backslash phi\; \backslash ,$. :$\backslash phi\; =\; f/P\; \backslash ,$ For nitrogen at 100 atm, the fugacity coefficient is 97.03 atm / 100 atm = 0.9703. For an ideal gas, fugacity and pressure are equal so $\backslash phi\; \backslash ,$ is 1. The contribution of nonideality to the chemical potential of a real gas is equal to RT ln $\backslash phi$. Again for nitrogen at 100 atm, the chemical potential is μ = μid + RT ln 0.9703, which is less than the ideal value μid because of intermolecular attractive forces. 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, Again using nitrogen at 100 atm as an example, since the fugacity is 97.03 atm, the activity is just 97.03 without units. 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. The word "fugacity" is derived from the Latin for "fleetness", which is often interpreted as "the tendency to flee or escape". The concept of fugacity was introduced by American chemist Gilbert N. Lewis in 1901. ==Definition in terms of chemical potential== The fugacity of a real gas is formally defined by an equation analogous to the relation between the chemical potential and the pressure of an ideal gas. or In general, the chemical potential (μ) is defined as the partial molar Gibbs free energy. However, for any pure substance it is equal to the molar Gibbs free energy, and its variation with temperature (T) and pressure (P) is given by $=\; dG\; =\; -SdT\; +\; VdP$. At constant temperature, this expression can be integrated as a function of $P$. We must also set a reference state. For an ideal gas the reference state depends only on pressure, and we set $P$ = 1 bar so that :$\backslash int\_^\backslash mu\; =\; \backslash int\_^P$ Now, for an ideal gas $\backslash bar\; V\; =\; \backslash frac$ :$\backslash mu\; -\; \backslash mu\; ^\backslash circ\; =\; \backslash int\_^P\; =\; RT\backslash ln\; \backslash frac$ Reordering, we get :$\backslash mu\; =\; \backslash mu\; ^\backslash circ\; +\; RT\backslash ln\; \backslash frac$ This gives the chemical potential for an ideal gas in an isothermal process, with a reference state is $P$ = 1 bar. For a real gas, the integral $\backslash int\_^P$ cannot be calculated because there isn't a simple expression for a real gas's molar volume. Even if using an approximate expression such as the van der Waals equation, the Redlich–Kwong or any other equation of state, it would depend on the substance being studied and would be therefore of very limited utility. Additionally, chemical potential is not mathematically well behaved. It approaches negative infinity as pressure approaches zero and this creates problems in doing real calculations. It is desirable that the expression for a real gas’ chemical potential to be similar to the one for an ideal gas. Therefore one can define a quantity, called fugacity, so that the chemical potential for a real gas becomes :$\backslash mu\; =\; \backslash mu\; ^\backslash circ\; +\; RT\backslash ln\; \backslash frac$ with a given reference state to be discussed later. This is the usual form of the definition, but it may be solved for f to obtain the equivalent explicit form :$f\; =\; \backslash exp\; \backslash left(\backslash frac\backslash right)$ 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「fugacity」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.