16 - Chem 204 Lecture 16 We have been looking at galvanic...

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Chem 204 Ͳ Lecture 16 ± We have been looking at galvanic cells to get E° and ǻ G°, but what happens as cell operates? ± Eventually we will use up reactants, generate products and system will reach equilibrium. ± ǻ G =0= ǻ G°+RTlnQ=-RT lnK+ RT lnQ; (Q=K) ± So E must decrease as cell runs down± ± But ǻ G = -nFE = -nFE° + RT ln Q or± ± E = E° - (RT/nF) ln Q ² Nernst Equation ± Remember n = # of e - in the balanced redox rxn. ± We can now predict E under non-std. conditions.
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Lecture 16 ±Page 2 ± At 298 K, since R and F are constants, we write ± E = E° - (2.57x10 -2 /n) ln Q (2 nd term in Volts) or ± E = E° - (5.92x10 -2 /n) log 10 Q (2 nd term in Volts) ± So if you make a cell with known concentrations and/or pressures of the species involved, you can determine Q, and with E°, you can get E. ± But there is an added bonus, if you have a rxn, where it may be difficult to determine E°, you can measure E, and with Q known, get E°! ±
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Lecture 16 ±Page 3 ± Why are these important? If determining E° or Q explicitly are difficult (perhaps with respect to experimental conditions), using ± E° = E + (2.57x10 -2 /n) ln Q = (2.57x10 -2 /n) ln K. ±
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This note was uploaded on 11/19/2010 for the course CHEM 204 taught by Professor Gruebele during the Spring '08 term at University of Illinois, Urbana Champaign.

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16 - Chem 204 Lecture 16 We have been looking at galvanic...

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