Lecture 33 111408 - • Effect of temperature depends on...

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Free Energy S universe  > 0 means thermodynamically  allowed Free energy or Gibbs Free Energy(G)  defined by G = H-TS G is a state function (H, T and S are state  functions) For reaction at Constant Temperature G =  H – T S
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Introduction to Free Energy Gibbs Free Energy Change ( G ):  Weighs the relative  contributions of  enthalpy  and  entropy  to the overall  spontaneity of a process. G is a state function Sign of  G tells us if a reaction is allowed G  =  H  –  T S G  < 0 Process is spontaneous G  = 0 Process is at equilibrium G  > 0 Process is nonspontaneous
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Roles of  H and  S Form of  G shows role of  H and  S in  spontaneity H<0 exothermic, favors reaction S>0  more entropy, favors reaction Role of T Usually assume  H and  S do not depend on  T.  T S term varies with T
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Unformatted text preview: • Effect of temperature depends on signs ∆ G = ∆ H – T ∆ S Introduction to Free Energy Introduction to Free Energy CaCO 3 (s) → CaO(s) + CO 2 (g) ∆ Hº = 178.3 kJ ∆ Sº = 160 J/K 1. Is the reaction spontaneous under standard conditions at 25 ºC ∆ G = ∆ H - T ∆ S 2. Calculate the temperature at which the reaction becomes spontaneous The changeover point between spontaneous and nonspontaneous is when ∆ G =0 Entropy of Vaporization • ∆ S vap = ∆ H vap /T • Units J/molK • Benzene, C 6 H 6 , has an enthalpy of vaporization, ∆ H vap , equal to 30.8 kJ/mol and boils at 80.1°C . What is the entropy of vaporization, ∆ S vap , for benzene? • Entropy increases as system boils...
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This note was uploaded on 08/29/2010 for the course CHM 2045 taught by Professor Brant during the Fall '08 term at University of South Florida.

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Lecture 33 111408 - • Effect of temperature depends on...

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