Lecture 8 Cell Make-up and Cell Potential

Lecture 8 Cell Make-up and Cell Potential -...

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Cell Potential (E cell ) The cell potential ( E cell ) is a fundamental property of electrochemical cells. E cell is measured in Volts (V), where V = J/C (a coulomb, C , is a unit of charge) E cell > 0 for a spontaneous process Zn( s )+Cu 2+ ( aq ) Zn 2+ ( aq )+Cu( s ) The standard potential ( E ° cell ) is the cell potential in standard conditions (i.e., 25 ° C, 1 M solutes, etc.) If E° is positive (spontaneous flow of e ), the cell is voltaic (= galvanic) If E° is negative (nonspontaneous flow of e ), the cell is electrolytic .
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Electrochemical Cells The cell potential of any electrochemical cell is the sum of the half cell potentials for the oxidation and reduction half cells. E cell = E oxidation + E reduction For example, if given the following information: Pb 2+ (aq) + 2 e Pb(s) E red = 0.13 V Cu(s) Cu 2+ (aq) + 2 e E ox = 0.34 V Pb 2+ (aq) + Cu(s) Pb(s) + Cu 2+ (aq) E° = -0.47 V
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Electrochemical Cells 3 Pb 2+ (aq) + 2 Al(s) 3 Pb(s) + 2 Al 3+ (aq) For a given process, the half-cell potentials for oxidation (E ox ) and reduction (E red ) have the same magnitude, but opposite charge. For example: Al 3+ (aq) + 3 e - Al(s) red = -1.66V Al(s) Al 3+ (aq) + 3 e - ox = 1.66V As you recall, when you balance an electrochemical reaction, half-cell reactions should be multiplied to cancel the electrons. For example: 3×[ Pb 2+ (aq) + 2 e - Pb(s)] red = -0.13V 2×[ Al(s) Al 3+ (aq) + 3 e - ]E ° ox = +1.66V Note that , the half-cell potentials are NOT MULTIPLIED , as E is an intensive property.
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This note was uploaded on 12/15/2011 for the course CHM 139 taught by Professor Browning during the Spring '08 term at University of Toronto- Toronto.

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Lecture 8 Cell Make-up and Cell Potential -...

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