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Dependence of Cell Potential on Concentration

Dependence of Cell Potential on Concentration. Voltaic cells at NONstandard conditions -- LeChatlier’s principle can be applied. An increase in the concentration of a reactant will favor the forward reaction and the cell potential will increase . The converse is also true! .

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Dependence of Cell Potential on Concentration

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  1. Dependence of Cell Potential on Concentration Voltaic cells at NONstandard conditions -- LeChatlier’s principle can be applied. An increase in the concentration of a reactant will favor the forward reaction and the cell potential will increase. The converse is also true!

  2. When cell is not at standard conditions, use Nernst Equation E = Eo – RT ln Q nF R = Gas constant 8.315 J/K mol F = Faraday constant Q = reaction quotient [productscoefficient]/[reactantscoefficient] E = Energy produced by reaction T = Temperature in Kelvins n = # of electrons exchanged in BALANCED redox equation

  3. Rearranged, another useful form NERNST EQUATION: E = E° - 0.0592 log Q@ 25°C(298K) n

  4. As E declines with reactants converting to products, E eventually reaches zero. Zero potential means reaction is at equilibrium [dead battery]. Also, Q = K AND G = 0 as well.

  5. Notice the difference in the concentrations pictured at the left.

  6. Because the right compartment contains 1.0 M Ag+ and the left compartment contains 0.10 M Ag+, there will be a driving force to transfer electrons from left to right.

  7. Silver will be deposited on the right electrode, thus lowering the concentration of Ag+ in the right compartment. In the left compartment the silver electrode dissolves [producing Ag+ ions] to raise the concentration of Ag+ in solution.

  8. Concentration cells e- e- Ag Ag • Electrons will move from 0.1 M Ag+ to 1 M Ag+ • Pull Ag+ from 1M side—plating metal • Taking e- from Ag electrode will produce more Ag+ on 0.1 M side 0.1 M Ag+ 1.0 M Ag+

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