L27S07_ThermoSecondLaw 03-21-07

L27S07_ThermoSecondLaw 03-21-07 - Chem 1A L27"Entropy...

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Unformatted text preview: Chem 1A, L27: "Entropy, Second Law" Bond Dissociation Energies X Summary Ex-y Ex- Y X + Y X + Y X Y Bond Energies and Reaction Enthalpies Atoms Ex-y(R) E -Ex-y(P) E -Ex-y Ex- Reactants H H= Ex-y(R) -Ex-y(P) Products L21-6 A.Pines,M.Kubinec,UCB L21-4 A.Pines,M.Kubinec,UCB A.Pines,M.Kubinec,UC L27-1 Spontaneous Process The Reverse Never Occurs The Second Law (You can't break even) For any process: Summary warm hot A.Pines,M.Kubinec,UC Pressure Equilibration Temperature Equilibration E = 0 w = 0 q = 0 S = kB ln W warm cool S > 0 q S = rev T L29-4 Suniv = Ssys + Ssurr ? 0 > 0 : Spontaneous, Irreversible = 0 : Reversible, Equilibrium < 0 : Not Possible 2000 University of California L20-5 Isothermal Expansion/Compression Pext = F/A Adiabatic Expansion/Compression Pext = F/A Const T : E = H = 0 q + ww 0 =- = hhExpansion w<0 q>0 S > 0 Compression w>0 q<0 S < 0 L20-6 q = 0 : E = w hhExpansion w<0 q=0 S > 0 2000 University of California Compression w>0 q=0 S > 0 L20-7 2000 University of California Spontaneous Process The Reverse Never Occurs Pressure Equilibration Temperature Equilibration E = 0 w = 0 q = 0 S = kB ln W warm hot A.Pines,M.Kubinec,UC warm cool S > 0 q S = rev T L27-3 A.Pines,M.Kubinec,UC 1 Chem 1A, L27: "Entropy, Second Law" ChemQuiz 27.1 Consider six distinguishable objects in two boxes. How many ways can you have 4 in the left box? box? 1 2 5 3 4 6 1) 6 A.Pines,M.Kubinec,UC 2) 15 3) 36 L27-4 The Second Law (You can't break even) can' For any process: Suniv = Ssys + Ssurr 0 > 0 : Spontaneous, Irreversible = 0 : Reversible, Equilibrium < 0 : Not Possible A.Pines,M.Kubinec,UC L27-6 ChemQuiz 27.2 Which process is accompanied by the greatest increase in entropy (S)? 1 2 3 A) 1 A.Pines,M.Kubinec,UC 2 B) 2 3 C) 3 1 L27-7 A.Pines,M.Kubinec,UC 2 Chem 1A, L27: "Entropy, Second Law" Isothermal Expansion/Compression PextP= F/A ext Const T : E = H = 0 q + ww 0 =- = h+ Expansion V > O wO Expansion w<0 q>0 S > 0 L27-9 A.Pines,M.Kubinec,UC Isothermal Expansion/Compression Pext Const T : E = H = 0 q + ww 0 =- = hExpansion w<0 q>0 S > 0 Compression w>0 q<0 S < 0 L27-10 A.Pines,M.Kubinec,UC Adiabatic Expansion/Compression Pext q = 0 : E = w Expansion V > O wO h+ Expansion w<0 q=0 S > 0 L27-11 A.Pines,M.Kubinec,UC A.Pines,M.Kubinec,UC 3 Chem 1A, L27: "Entropy, Second Law" Adiabatic Expansion/Compression Pext q = 0 : E = w hExpansion w<0 q=0 S > 0 A.Pines,M.Kubinec,UC Compression w>0 q=0 S > 0 L27-12 ChemQuiz 27.3 An ideal gas expands isothermally against a vacuum. What is Ssurr ? vacuum. Pext = 0 Expansion V > O wO h+ 1) < 0 A.Pines,M.Kubinec,UC 2) = 0 3) > 0 L27-13 ChemQuiz 27.4 An ideal gas is isothermally compressed. What is Ssurr ? h- 1) < 0 A.Pines,M.Kubinec,UC 2) = 0 3) > 0 L27-15 A.Pines,M.Kubinec,UC 4 Chem 1A, L27: "Entropy, Second Law" Phase Transition (Order Hvap H2 O Hvap Tbp vap liq Disorder) qrev T Vaporization of a liquid at Tbp S = 40 kJ 100 C A.Pines,M.Kubinec,UC Tbp Hvap S = Tbp Svap ~ 90 J/K mol (H2O ~ 110 J/K mol) L27-17 Lecture Complete A.Pines,M.Kubinec,UC L27-18 A.Pines,M.Kubinec,UC 5 ...
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This note was uploaded on 08/19/2009 for the course CHEM 1A taught by Professor Nitsche during the Spring '08 term at Berkeley.

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