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Information about Fugacity and determinatn

For MSc Part I sem 1 students

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What is Fugacity G.N. Lewis introduced the concept of “Fugacity’’ (1901) Work function and Free energy relationship, For an isothermal work of expansion, At constant temperature, dF = VdP …(1) For system consists of 1 mole of an ideal gas V= Therefore, dF = RT dF = RT d In P …(2) For real gases, dF = RT d In f …(3) Where f is called Fugacity It may be defined, as such manner that below equation is satisfied F = RT In f + C …(4)

More precisely in terms of relative fugacity, F2 - F1 = RT In …(5) At very low pressure the ratio f/P reaches to unity; =1 1 as p 0

Graphical Method The deviation of real gas from ideal behavior can be determined by this method from equation (1) and (3) RTd in f = VdP T …(6) …(7) Then for a real gas quantity α defined by, α Hence from equation (6) RTd In f = RT …(8)

(Cont) Hence from equation (6) RTd In f = RT d In f = d In P d In =- dP dP

If this result is integrated between a low virtually zero, pressure and given pressure P, at a constant temperature the result is In =- Or In = In P - …(9)

Approximate calculation of Fugacity From Van der Waals equation, when pressure is low the value PV for any gas is a linear function at constant temperature PV = RT – AP (Where A is constant) From equation (8), α =A From this result, In f = In P In = - …(10)

At moderate pressure f/P is not very different from unity hence, equation (10) become, -1=Upon introducing the definition of α is f= …(11) But, Pid = = …(12)

Fugacity and determinatn 1. - Aashitosh. Solanki 2. What is Fugacity G.N. Lewis introduced the concept of “Fugacity’’ (1901) Work function and ...

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