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Chem208_Lecture_25_BW

Chem208_Lecture_25_BW - E° is a state function ∆ G° =...

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1 Today: Electrochemistry (Ch. 20) - Galvanic Cells - Read section 20-5 (Batteries) PS10 is due Friday, 4/25, at 2:00
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2 Introducing Aurora Davis, born 4/19/08
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3 At anode : oxidation half reaction occurs here; electrons are lost At cathode : reduction half reaction occurs here; electrons are gained Review
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4 Relationship between G and E w elec = nFE (work done by the system) n: # of moles of electrons transferred F: charge on 1 mole of electrons (the Faraday) (F = 96,485 coulombs) E: cell potential
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5 From thermodynamics, G = -w So, G = –nFE Under standard conditions: G° = –nFE°
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6 How much of the 0.46 volt is a measure of the tendency for Ag + to be reduced to Ag, and how much is a measure of the tendency for Cu to be oxidized to Cu 2+ ? Problem: E° can not be measured for a half reaction
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7 Standard Hydrogen Electrode (SHE) 2 H 3 O + ( aq ) + 2 e H 2 ( g ) E° = 0.00 volt Both the selection of the SHE and the assignment of E°=0.00 volt are completely arbitrary!
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Unformatted text preview: E° is a state function ( ∆ G° = –nFE°). Consequently, E° (R → P) = –E°( P → R) 8 9 Should Cu 2+ oxidize Al under standard conditions? From Table of Standard Reduction Potentials: Cu 2+ (aq) + 2 e – → Cu (s) E° = +0.340 volt Al 3+ (aq) + 3±e – → Al (s) E° = -1.676 volt 10 Terry’s First, and so far only, Law Just because something should occur doesn’t mean it will occur; and even if it does occur, it will not necessarily occur as rapidly as we might wish. 11 Cell Potential under any conditions: The Nernst Equation ∆ G = -nFE and ∆ G = ∆ G° + RTlnQ 12 Start with the standard Cu/Ag cell. Allow a current of 1.0 amp to flow for 2.0 hours. (1 amp = 1 coulomb/sec) Calculate: (a) the change in mass for each electrode and (b) the cell potential, E cell after the two hours have passed....
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Chem208_Lecture_25_BW - E° is a state function ∆ G° =...

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