Chem_215_Lect_25_Color - Cell Potential(Ecell G and K The...

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1 Cell Potential (E cell ), G, and K The standard Gibbs Free Energy Change, ( G o ) is related to K by: G o = - RT lnK = - nFE o cell K g o l n 0.0591V K n l n 0.025693V K n l nF RT E 10 o cell = = =
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2 Cell Potential (E cell ), G, and K eq K g o l n 0.0591 E 10 o cell = Calculate the standard cell potential E o cell for: Pt|Fe 2+ ,Fe 3+ ||Ag + |Ag(s) What is the equilibrium constant K eq ? E o cell = 0.029 V K eq = 3.09 0.0591 nE K g o l o cell 10 =
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3 Combining Half Reactions • Given: Fe 3+ (aq) + e - Fe 2+ (aq) E o = 0.771 V Fe 2+ (aq) +2e - Fe(s) E o = -0.440 V Fe 3+ (aq) + 3e - Fe(s) What is the reduction potential for: Fe 3+ (aq) + 3e - Fe(s) E o = ?
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4 Combining Half Reactions: Use G o = -nFE o Given: Fe 3+ (aq) + e - Fe 2+ (aq) E o = 0.771 V Fe 2+ (aq) +2e - Fe(s) E o =-0.440 V Fe 3+ (aq) + 3e - Fe(s) → ∆ G o = -1 x F x E o = -74.38kJ → ∆ G o = -2 x F x E o = 84.91kJ V 0363 . 0 3(96,485C) - J 10.52x10 nF G E 3 o o = = = G o = -74.38kJ + 84.91 kJ = 10.52 kJ A cell reduction potential E o is not a state function. For Hess’ law calculations, we require a quantity that is a state function, in this case use G o = -nFE o.
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