L27S09_FreeEnergy1+04-01-09

L27S09_FreeEnergy1+04-01-09 - Chem 1A Lecture 27:...

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Unformatted text preview: Chem 1A Lecture 27: "Free Energy; Direction of Change" 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 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 © 2000 University of California ©A.Pines,M.Kubinec,UCB L27-1 L20-7 ChemQuiz© 27.1 An ideal gas is isothermally compressed. What is ∆Ssurr ? ∆h- A) < 0 ©A.Pines,M.Kubinec,UCB B) = 0 C) > 0 L27-2 Summary Summary ∆G = ∆H -T∆S ∆H > 0 Endothermic ∆H > 0 Endothermic ∆H ∆S <0 <0 Exothermic More order No T Low T High T All T ∆H ∆S ∆S > 0 Less order ∆S > 0 Less order ©A.Pines,M.Kubinec,UCB L24-7 ©A.Pines,M.Kubinec,UCB 1 Chem 1A Lecture 27: "Free Energy; Direction of Change" Phase Transition (Order ∆Hºvap H2 O ∆Hºvap Tbp vap liq Disorder) qrev T Vaporization of a liquid at Tbp ∆Sº = 40 kJ 100 ºC ©A.Pines,M.Kubinec,UCB Tbp ∆Hºvap ∆Sº = Tbp ∆Sºvap ~ 90 J/K mol J/K (H2O ~ 110 J/K mol) L27-5 ChemQuiz© 27.2 At the Triple Point of water, ice, liquid and ice, vapor are all in equilibrium. Which transition involves the greatest increase in entropy? A) S L ©A.Pines,M.Kubinec,UCB H 2O L S G Temperature Tc P B) L G C) G S L27-6 Triple Point of Water H2O (g) H2O (l) H2O (s) Equilibrium = universe is indifferent liquid ∆SSys ∆HSurr ∆HSurr ∆SSys L27-8 ©A.Pines,M.Kubinec,UCB ©A.Pines,M.Kubinec,UCB 2 Chem 1A Lecture 27: "Free Energy; Direction of Change" Tracking the Entropy of the Universe H2O (l) H2O (g) ∆Ssurr + ∆Ssys = ∆Suniv ≥ 0 ∆Hvap + ∆Ssys = ∆Suniv T ∆G ≤ univ ∆Hsys – T ∆Ssys= -T ∆S0 ≤ 0 ©A.Pines,M.Kubinec,UCB L27-9 Gibbs Free Energy G = H - TS ∆Gº = ∆Hº -T∆Sº Spontaneous Process H S G ∆G < O ∆Gº = Σ ∆Gfº(Products) – Σ ∆Gfº(Reactants) ©A.Pines,M.Kubinec,UCB L27-10 Free Energy Space ∆G = ∆H -T∆S ∆H > 0 Endothermic ∆H ∆S <0 <0 Exothermic More order No T Low T High T All T ∆H ∆S ∆ S > 0 Less order ∆S > 0 Less order ©A.Pines,M.Kubinec,UCB L27-11 ©A.Pines,M.Kubinec,UCB 3 Chem 1A Lecture 27: "Free Energy; Direction of Change" ChemQuiz© 27.3 The reaction shown is spontaneous at 25 °C. ∆H° for the reaction is: 2 NO2 (g) N2O4 (g) A) < 0 ©A.Pines,M.Kubinec,UCB B) = 0 C) > 0 L27-12 ChemQuiz© 27.4 Which is the correct plot of ∆G° vs. T for the reaction H2O (l) H2O (g)? (l) (g)? A) ∆G° T H 2O L S G Temperature Tc P B) ∆G° C) T ∆G° T ©A.Pines,M.Kubinec,UCB L27-14 Thermodynamic Parameters kJ/mol J/K mol kJ/mol ∆H°f S° ∆G°f ∆H°f S° C(s) Mg(s) kJ/mol J/K mol ∆G°f kJ/mol H2(g) O2(g) 0 0 131 205 0 0 0 0 6 33 0 0 –569 CO2(g) –394 214 –394 H2O(g) –242 189 –229 H2O(l) –286 70 –257 ©A.Pines,M.Kubinec,UCB MgO(s) –602 29 MgO(s) C2H2(g) 229 CH3CH2OH(l) –298 201 209 161 –175 L27-16 ©A.Pines,M.Kubinec,UCB 4 Chem 1A Lecture 27: "Free Energy; Direction of Change" Free Energy and Reactions ∆H ∆S ∆G K (s) + H20 (l) (s) (l) H2O(l) + ½O2(g) AlBr3 (s) (s) K+ (aq) + OH- (aq) + ½ H2 (g) aq) aq) (g) H2O2(l) -+- + -+ +++ + --L27-17 Al (s) + 3/2 Br2 (l) (s) 3/2 (l) 2 MgO (s) + C (s) (s) 2 Mg (s) + CO2 (s) (s) (s) ©A.Pines,M.Kubinec,UCB ChemQuiz© 27.5 CO2 (g) + CaO (s) CaCO3 (s) ∆H˚ ~ -200 KJ · mol-1 ∆S˚~ -200 J mol-1K-1 For the reaction: For what temperature range is the reaction spontaneous? spontaneous? A) < 1000 ©A.Pines,M.Kubinec,UCB B) ~ 1000 C) > 1000 L27-18 Lecture Complete ©A.Pines,M.Kubinec,UCB L27-20 ©A.Pines,M.Kubinec,UCB 5 ...
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