Chapter-20-2 - Ecell and Grxn A + Bn+ An+ + B transfer of n...

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1 E º cell and G º rxn A + B n + A n + + B transfer of n moles e- is spontaneous if cell > 0 and/or rxn < 0 rxn = - n F Eº cell chemical free energy electrical energy used to move n moles e- F = Faraday constant charge of 1 mole e- 96485 C
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2 electric energy = charge potential (voltage) 1 J = 1 C 1 V (joule) (coulomb) (volt) 1 eV = 1.6 10 -19 C 1 V (electron-volt)
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3 Zn | Zn 2+ || Cu 2+ | Cu Zn + Cu 2+ Zn 2+ + Cu cell = + 1.10 V rxn = - 2 F Eº cell = -212 kJ i.e. spontaneous and complete reaction note: Gº depends on n (stoichiometry of reaction) cell does not
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4 Eº, Gº, Hº, Sº for standard conditions [i] = 1 M P i = 1 atm
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5 The Nernst equation conditions change during operation of cell zinc-copper cell Zn + Cu 2+ Zn 2+ + Cu [Zn 2+ ] [Cu 2+ ] generally, a cell operates under non-standard conditions with [i] 1 M G rxn = - n F E cell
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6 G rxn = - n F E cell = RT ln(Q/K) E cell = - (RT/ n F) ln(Q/K) = (RT/ n F) lnK - (RT/ n F) lnQ E cell = cell - (RT/ n F) lnQ Nernst equation T = 298 K F = 96485 C R = 8.314 J K -1 mol -1 E cell = cell - (0.0257/ n ) lnQ E cell = cell - (0.0592/ n ) logQ E in volts
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zinc-silver cell Zn + 2 Ag + Zn 2+ + 2 Ag cell = + 1.56 V Q = [Zn 2+ ]/[Ag + ] 2 E cell =
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This note was uploaded on 02/17/2011 for the course ENGINEERIN chem 1e03 taught by Professor Aaa during the Spring '11 term at McMaster University.

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Chapter-20-2 - Ecell and Grxn A + Bn+ An+ + B transfer of n...

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