notes_Lecture_09_102010

notes_Lecture_09_102010 - Lecture 9: Gibbs Free Energy...

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Unformatted text preview: Lecture 9: Gibbs Free Energy Reading: Zumdahl 10.7, 10.8 and 10.9 Outline Define Gibbs free energy (10.7) a formulation of S univ in terms of system variables Free energy and chemical reactions (10.9) Second Law of Thermodynamics Define: S sys + S surr = S univ 1. S univ > 0 process is spontaneous 2. S univ < 0 process is spontaneous in opposite direction 3. S univ = 0 process is at equilibrium We need to know S for BOTH the system and surroundings to predict if a reaction will be spontaneous! The entropy of the universe is always increasing . In any spontaneous process , there is always an increase in the entropy of the universe . S surr = - H sys T S sys + S surr = S univ H sys < 0 S H sys < 0 S H sys > 0 S S surr = - H sys T Exothermic, Spontaneous Exothermic, Spontaneous Endothermic, Spontaneous Gibbs Free Energy ( G) Recall, the second law of thermodynamics: S univ = S system + S surr Also recall: S surr = - H sys /T Then , S univ = S system + S surr- H sys /T-T S univ = -T S system + H sys We then define a new function: G = -T S univ x (-T) Defining G (cont.) G = -T S univ = -T S sys + H sys Then: Or : G = H - T S G = -T S sys + H sys G = The Gibbs Free Energy w/ P const Note the absence of subscripts hereall quantities refer to the system . G and Spontaneous Processes...
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notes_Lecture_09_102010 - Lecture 9: Gibbs Free Energy...

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