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Unformatted text preview: Lecture 28 1 Lecture 28 - Thermodynamic Equilibrium Constant (26.11-12) In the previous lecture, we introduced a thermodynamic equilibrium constant based on fugacities: where and Y Z Y Z Y Z A B A B A B v v v v v v Y Z Y Z Y Z f P P v v v v v v A B A B A B f f P P K K K K K f f P P = = = = Remember, the physical observable we measure is pressure, but the equilibrium constant is based on fugacities. We need a more general relation to cover not only gases, but liquids, solids and solutions (i.e. multicomponent, multiphase, reacting systems!) We need to start somewhereso lets begin with our basic definitions. Weve got liquids and solutions down pat: ( 29 ln activity of component . o j j j j T RT a a j = + = For solutions with solvent and solute this is well-defined: as 1 Raoult's law Standard State , as , 0 Henry's law Standard State j j j j j j j j a x x a c m c m Lecture 28 2 We can readily extend this form for gases by letting where fugacity of component . j j o j i f a f f j = For arbitrary states and phases for reactants and products: A B Y Z v A v B v Y v Z + + ln where Y Z A B v v o Y Z r Y Y Z Z A A B B r v v A B o o o o o r Y Y Z Z A A B B a a G v v v v G RT a a G v v v v = +-- = + = +-- This is the Lewis Equation. Lewis & Pitzer were the two 20 th century giants of thermodynamics. They wrote the classic thermodynamics text book used by generations. Again as before: Y Z A B v v Y Z a v v A B a a Q a a = A Now by definition 1 when substances are in their standard states....
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