L26S10_ThermoSecondLaw+03-29-10

L26S10_ThermoSecondLaw+03-29-10 - Chem 1A, L26:...

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Unformatted text preview: Chem 1A, L26: "Entropy, Second Law" Lab 8: Products and Reactants Goal: Observe, predict and record Observe, the response of reactions in equilibrium. equilibrium. Tools and Skills: : Equilibria, Equilibria, Le Chatelier's Principle © A.Pines,M.Kubinec,UC L26-1 Bond Dissociation Energies X Summary Ex-y Y X Y X Y X Y Bond Energies and Bond Reaction Enthalpies Reaction Atoms Ex-y(R) E -Ex-y(P) E -Ex-y 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 L26-2 ChemQuiz ChemQuiz© 25.4 The decomposition: H2 O 2 H2 O 1/2 O2 is exothermic is exothermic. What is the molecular molecular structure of H2O2? A) H OO H B) H O=O H C) H O=O C) B) H L26-3 © A.Pines,M.Kubinec,UC © A.Pines,M.Kubinec,UC 1 Chem 1A, L26: "Entropy, Second Law" Spontaneous Process The Reverse Never Occurs The 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= S>0 qrev T L29-4 I sothermal Isothermal Expansion/Compression Expansion/Compression Pext = F/A Adiabatic Adiabatic Expansion/Compression Expansion/Compression Pext = F/A Const T : Const h- E= H=0 q + ww 0 =- = Expansion w<0 q>0 S>0 © 2000 University of California q=0: hExpansion w<0 q=0 S>0 E=w Compression w>0 q=0 S>0 L20-7 Compression w>0 q<0 S<0 L20-6 © 2000 University of California Spontaneous Process The Reverse Never Occurs Pressure Equilibration Temperature Equilibration E=0 w=0 q=0 S = kB ln W ln warm hot hot © A.Pines,M.Kubinec,UC warm cool S>0 q S = rev T L26-6 ChemQuiz© 26.1 Consider six Consider six distinguishable objects in two boxes. How How many ways can you have 4 in the left box? box? 1 2 5 3 4 6 A) A) 6 © A.Pines,M.Kubinec,UC B) B) 15 C) C) 36 L26-7 © A.Pines,M.Kubinec,UC 2 Chem 1A, L26: "Entropy, Second Law" The Second Law (You can t break even) For any For any process: Suniv = Ssys + Ssurr 0 > 0 : Spontaneous, Irreversible = 0 : Reversible, Equilibrium Reversible, < 0 : Not Possible © A.Pines,M.Kubinec,UC L26-9 ChemQuiz© 26.2 Which Which process is accompanied by the greatest greatest increase in in entropy ( S)? 1 2 3 A) A) 1 © A.Pines,M.Kubinec,UC 2 B) 2 B) 3 C) 3 C) 1 L26-10 Isothermal Isothermal Expansion/Compression Expansion/Compression PextP= F/A ext Const T : Const h+ E= H=0 q + ww 0 =- = Expansion V>O wO © A.Pines,M.Kubinec,UC Expansion w<0 q>0 S>0 L26-12 © A.Pines,M.Kubinec,UC 3 Chem 1A, L26: "Entropy, Second Law" Isothermal Isothermal Expansion/Compression Expansion/Compression Pext Const T : Const h- E= H=0 q + ww 0 =- = Expansion w<0 q>0 S>0 © A.Pines,M.Kubinec,UC Compression w>0 q<0 S<0 L26-13 ChemQuiz© 26.3 An An ideal gas expands expands isothermally against isothermally against a vacuum vacuum. What is Ssurr ? Pext = 0 Expansion V>O wO h+ A) A) < 0 © A.Pines,M.Kubinec,UC B) = 0 B) C) > 0 C) L26-14 ChemQuiz© 26.4 An An ideal gas is isothermally compressed. isothermally compressed. What What is Ssurr ? h- A) A) < 0 © A.Pines,M.Kubinec,UC B) = 0 B) C) > 0 C) L26-16 © A.Pines,M.Kubinec,UC 4 Chem 1A, L26: "Entropy, Second Law" Adiabatic Adiabatic Expansion/Compression Expansion/Compression Pext q=0: Expansion V>O wO © A.Pines,M.Kubinec,UC E=w h+ Expansion w<0 q=0 S>0 L26-18 Adiabatic Adiabatic Expansion/Compression Expansion/Compression Pext q=0: hExpansion w<0 q=0 S>0 © A.Pines,M.Kubinec,UC E=w Compression w>0 q=0 S>0 L26-19 Phase Transition (Order Hºvap H2 O Hºvap Tbp Disorder) qrev T Vaporization Vaporization of a liquid at Tbp Sº = Sº = 40 kJ 100 ºC © A.Pines,M.Kubinec,UC Tbp Hºvap Tbp º S vap ~ 90 J/K mol 90 J/K (H2O ~ 110 J/K mol) L26-20 © A.Pines,M.Kubinec,UC 5 Chem 1A, L26: "Entropy, Second Law" Lecture Complete © A.Pines,M.Kubinec,UC L26-21 © A.Pines,M.Kubinec,UC 6 ...
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