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L39S07_CellPotFreeEnergy 04-25-07

L39S07_CellPotFreeEnergy 04-25-07 - CHEM 1A...

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Unformatted text preview: CHEM 1A, L-39: "Galvanic Cells; Free Energy and Cell Potential;" Fall 04, Prof. Nitsche Redox and Electrochemistry Standard Galvanic Cell Cu2+ (aq) + Zn (s) aq) oxidizer reducer Cu2+ (aq) + Zn (s) aq) Previously oxidizer ? Zn2+ (aq) + Cu (s) aq) Zn2+ (aq) + Cu (s) aq) reducer ? Anode - e- e- + Cathode Zn2+ 1.0 M Oxidation Zn Zn2+ + 2 e- Salt Bridge Cu2+ 1.0 M Cu Reduction Spontaneous: G? < 0, K > 1 Zn Zn2+ + 2 eCu2+ + 2 eReduction Cu L39-4 Cu2+ + 2 e- Notation: Zn Zn2+ (1.0 M) Cu2+ (1.0 M) Cu Oxidation A.Pines,M.Kubinec,UCB = 1.10 V A.Pines,M.Kubinec,UCB L39-5 Standard Reduction Potentials = Cu Zn = (right) (left) Standard Half-Cell Potentials HalfCu2+ + 2 e2 H+ + 2 eZn2+ + 2 eCu H2 Zn = +0.34 V +0.34 1.00 atm SHE: 2 H + 2 + + + Oxidizer H2 (g) Pt (V) eH2 (g) 0.00 Reducer = +0.00 V +0.00 - Pt H2 H Cu2+ Cu + +0.34 + H+ 1.0 M A.Pines,M.Kubinec,UCB 2004 M. Kubinec, A. Pines + Pt H2 H+ Zn2+ Zn - -0.76 L39-5 A.Pines,M.Kubinec,UCB = -0.76 V L39-1 L39-3 Standard Reduction Potentials Cu2+ + 2 e2 H+ + 2 eZn2+ + 2 eCu H2 Zn = +0.34 V +0.34 = +0.00 V +0.00 = -0.76 V Reducer Oxidizer 2004 M. Kubinec, A. Pines L39-2 ChemQuiz 38.3 Which of the following will oxidize H2? H2 (g) Pt 1.00 atm Which of the following will be reduced by H2? 1) Cu2+ 2004 M. Kubinec, A. Pines H+ 1.0 M 2) Cu 3)Zn2+ 3)Zn L39-3 2004 M. Kubinec, A. Pines 1 CHEM 1A, L-39: "Galvanic Cells; Free Energy and Cell Potential;" Fall 04, Standard Reduction Potentials Prof. Nitsche (V) Balancing Redox Equations MnO4- + 8 H3O+ + 5 eAu+3 + 3 eO2 (g) + 4 H3O+ + 4 eBr2 (l) + 2 e- - Summary Au 6 H2O 2 BrAg 4 OHCu Mn2+ + 12 H2O +1.49 +1.42 +1.23 +1.06 +0.80 +0.40 +0.34 0.00 -0.23 -0.41 -0.76 -0.83 -2.36 -2.71 -2.76 MnO4- + 8 H3O+ + 5 eBr2 (l) + 2 e2 MnO4- + 16 H3O+ + 10 Br- - Mn2+ + 12 H2O x 2 10 e2 Brx 5 10 e5 Br2 (l) + 2 Mn2+ + 24 H2O Free energy and cell potential G = - nF eReducer Oxidizer A.Pines,M.Kubinec,UCB NO3- (g) + 4 H3O+ + 3 eAg+1 + 1 eO2 (g) + 2 H2O + 4 eCu+2 + 2 e2 H3O+ + 2 eNi+2 + 2 eFe+2 + 2 eZn+2 + 2 e2 H2O + 2 eMg+2 + 2 eNa+ + 1 eCa+2 + 2 e- NO (g) + 6 H2O +0.96 G L40-2 H2 + 2 H2O (l) Ni Fe Zn H2 + 2 OHMg Na Ca Examples Rusting of Iron - Fe Fe+2 OH- O2 Pt + = +0.81 V O2 + 2 Fe + 2 H2O 2 Fe+2 + 4 OHAutoioniztion of water - Pt H2 OH- H3O+ H2 Pt + = +0.83 V H3O+ + OHA.Pines,M.Kubinec,UCB 2 H2O L39-5 L40-3 2004 M. Kubinec, A. Pines Standard R e d u c ttio n P o te n tia lsPotentials Reduction S ta n d a r d io ta t ia (V ) M nO 4- + 8 H 3O + + 5 eA u +3 + 3 e O 2 (g ) + 4 H 3 O + + 4 e B r 2 (l) + 2 e N O 3 - (g ) + 4 H 3 O + + 3 e A g +1 + 1 e O 2 (g ) + 2 H 2 O + 4 e C u +2 + 2 e- M n 2+ + 12 H 2O Au 6 H 2O 2 B rN O (g ) + 6 H 2 O (g Ag 4 OHCu H 2 + 2 H 2 O (l) Ni Fe Zn H2 + 2 OHMg Na Ca + 1 .4 9 + 1 .4 2 + 1 .2 3 + 1 .0 6 + 0 .9 6 + 0 .8 0 + 0 .4 0 + 0 .3 4 0 .0 0 - 0 .2 3 - 0 .4 1 - 0 .7 6 - 0 .8 3 - 2 .3 6 - 2 .7 1 - 2 .7 6 L39-6 2 H 3O + + 2 e N i+ 2 + 2 e F e +2 + 2 e Z n +2 + 2 e 2 H 2O + 2 e M g +2 + 2 e N a+ + 1 eC a +2 + 2 e 2004 M. Kubinec, A. Pines Standard Reduction Potentials MnO4- + 8 H3O+ + 5 eAu+3 + 3 eO2 (g) + 4 H3O+ + 4 eBr2 (l) + 2 eNO3- (g) + 4 H3O+ + 3 eAg+1 Cu+2 +1 +2 eeeO2 (g) + 2 H2O + 4 Mn2+ + 12 H2O Au 6 H2O 2 BrNO (g) + 6 H2O Ag 4 OHCu (V) +1.49 +1.42 +1.23 +1.06 +0.96 +0.80 +0.40 +0.34 2004 M. Kubinec, A. Pines 2 Standard Reduction Potentials H3O+ + 2 eNi+2 + 2 eFe+2 + 2 eZn+2 + 2 e2 H2O + 2 Mg+2 Na+ +2 +1 eeeH2 + H2O (l) Ni Fe Zn H2 + 2 Mg Na Ca OH- CHEM 1A, L-39: "Galvanic Cells; Free Energy and Cell Potential;" Fall 04, Prof. Nitsche (V) -0.00 -0.23 -0.41 -0.76 -0.83 -2.36 -2.71 -2.76 L39-8 Ca+2 + 2 e 2004 M. Kubinec, A. Pines Balancing Redox Equations MnO4- + H3O+ + Br- Br2 (l) + Mn2+ + H2O MnO4- + 8 H3O+ + 5 e- Br2 (l) + 2 Bre- BrBr- + 2 e2 2 (l) Mn2+ + 12 H2O x 2 10 e- x 5 10 e- 2 MnO4- + 16 H3O+ + 10 Br- Free energy and cell potential 5 Br2 (l) + 2 Mn2+ + 24 H2O e- 0.43 V Reducer Oxidizer G L39-9 G = - nF 2004 M. Kubinec, A. Pines ChemQuiz 39.1 At what pH is = 0.50 V for the oxidation of Br- by MnO4- ? 1.0 M A) < O 2004 M. Kubinec, A. Pines B) = 0 C) > 0 L39-10 2004 M. Kubinec, A. Pines 3 CHEM 1A, L-39: "Galvanic Cells; Free Energy and Cell Potential;" Fall 04, Prof. Nitsche Examples Rusting of Iron O2 + Fe + H2O O2 (g) + 2 H2O + 4 e+2 Fex 2 2 e+ Fe O2 + 2 Fe + 2 H2O Fe+2 + OH4 OH+2 FeFe+ 2 e2 Fe+2 + 4 OH = +0.81 V L39-12 +0.40 -0.41 +0.41 Mg, Zn are sacrificial electrode for Fe 2004 M. Kubinec, A. Pines - Fe Fe+2 OH- O2 Pt + Examples Autoioniztion of water H3O+ + OH2 H3O+ + 2 e2 H2 O 2 OH-+ +2e H3O+ + OH2 H2O H2 + 2 H2O (l) H H2 2 + 2 2 2 + O OH- e2 H2O +0.00 V +0.83 V -0.83 V - Pt H2 OH- H3O+ H2 Pt + = +0.83 V 2004 M. Kubinec, A. Pines L39-13 ChemQuiz 39.2 Which of the following will oxidize Ni but not Ag? 1.0 M A) Br2 2004 M. Kubinec, A. Pines B) Cu C) H3O+ L39-14 2004 M. Kubinec, A. Pines 4 CHEM 1A, L-39: "Galvanic Cells; Free Energy and Cell Potential;" Fall 04, Prof. Nitsche ChemQuiz 39.3 Which of the following will be reduced by Zn but not by Br-? 1.0 M A) Au+3 2004 M. Kubinec, A. Pines B) Cu C) H3O+ L39-16 ChemQuiz 39.4 Which of the following will plate out on Cu from solution? 1.0 M A) Ca 2004 M. Kubinec, A. Pines B) Ag C) Au L39-18 Lecture Complete 2004 M. Kubinec, A. Pines L39-20 2004 M. Kubinec, A. Pines 5 ...
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