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 Δ S univ in terms of system variables – Free energy and chemical reactions (10.9) Second Law of Thermodynamics Define: Δ S sys + Δ S surr = Δ S univ 1. Δ S univ > 0 … process is spontaneous 2. Δ S univ < 0 … process is spontaneous in opposite direction 3. Δ S univ = 0 … process is at equilibrium We need to know Δ 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 . Δ S surr = -Δ H sys T Δ S sys + Δ S surr = Δ S univ Δ H sys < 0 S Δ H sys < 0 S Δ H sys > 0 S Δ S surr = -Δ H sys T Exothermic, Spontaneous Exothermic, Spontaneous Endothermic, Spontaneous Gibbs Free Energy ( Δ G) Recall, the second law of thermodynamics: Δ S univ = Δ S system + Δ S surr Also recall: Δ S surr = - Δ H sys /T Then , Δ S univ = Δ S system + Δ S surr- Δ H sys /T-T Δ S univ = -T Δ S system + Δ H sys We then define a new function: Δ G = -T Δ S univ x (-T) Defining Δ G (cont.) Δ G = -T Δ S univ = -T Δ S sys + Δ H sys Then: Or : Δ G = Δ H - T Δ S Δ G = -T Δ S sys + Δ H sys Δ G = The Gibbs Free Energy w/ P const Note the absence of subscripts here…all quantities refer to the system . Δ G and Spontaneous Processes...
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This note was uploaded on 09/29/2011 for the course CHM 101 taught by Professor Ma during the Spring '11 term at Beacon FL.

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notes_Lecture_09_102010 - Lecture 9 Gibbs Free Energy •...

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