Chem_215_Lect_24_Color - What is Eocell for a Standard...

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1 Cell Potentials: What is E o cell for a Standard Copper/Zinc Cell ? Cu 2+ (aq) + 2e - Cu (s) E o = 0.340V Zn 2+ (aq) + 2e - Zn (s) E o = -0.763V spontaneous E o cell = E o (cathode) – E o (anode) = 0.340 – (-0.763) = 1.103V Cu 2+ (aq) + 2e - Cu(s) Zn (s) Zn 2+ (aq) + 2e - Cu 2+ + Zn(s) Cu(s) + Zn 2+ + - In a galvanic cell: Anode (Oxidation) is Cathode (Reduction is +
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3 Cell Potential (E cell ) and Δ G The cell potential (E cell ) is related to the Gibbs Free Energy Change ( Δ G) for the reaction by: Δ G = -nFE cell where n = number of electrons transferred F = Faraday = 96,485 C/mole electrons Under standard conditions: Δ G o = -nFE o cell What is E o cell for the standard hydrogen-oxygen fuel cell: 2H 2 (g) + O 2 (g) 2H 2 O (l) Given: Δ G = - 474.2 kJ
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4 The Nernst Equation Recall that the nonstandard Gibbs Free Energy Change, ( Δ G) is related to Δ G o by: Δ G = Δ G o + RT lnQ Since Δ G = - nFE cell and Δ G o = - nFE o cell Therefore: - nFE cell = - nFE o cell + RT lnQ Q g o l n 0.0591 E Q n l nF RT E E 10 o cell o cell cell = =
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Chem_215_Lect_24_Color - What is Eocell for a Standard...

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