Lecture_4.ppt - Chemical Equilibrium All chemical reactions...

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Chemical Equilibrium All chemical reactions go in two directions, and reach an equilibrium in which the rates of reactions in both directions are equal. Chemical equilibrium is a dynamic state. Consider the chemical reaction: The equilibrium constant is given as: As talked before, in a dilute solution, we can assume that activity is equal to concentration. Therefore, dD cC bB aA b B a A d D c C eq a a a a K ] [ ] [ ] [ ] [ b a d c B A D C K ] [ ] [ ] [ ] [
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Equilibrium and Thermodynamics The equilibrium constant is derived from the thermodynamics of a chemical reaction. Enthalpy (H) : the enthalpy change (∆H) for a reaction is the heat absorbed or released. ∆H is positive – endothermic ∆H is negative – exothermic Entropy (S): S of a substance is a measure of its “disorder”. The greater the disorder, the greater the entropy. ∆S is the change in entropy.
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Free Energy Systems at constant pressure have a tendency toward lower enthalpy (∆H negative, liberation of heat) and higher entropy (∆S positive, increase in disorder). Free Energy: ∆G = ∆H - T ∆S Standard Free Energy: ∆G 0 = ∆H 0 - T ∆S 0 Free energy and equilibrium: Where R is the gas constant [= 8.314472 J/(K.mol)] and T is the temperature in kelvins.
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