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The standard cell potential is dependent on how different the concentrations in each of the half-cells are, as that is what generates the potential difference that allows a reaction to proceed in a certain direction. Standard cell potential is zero when the concentrations are the same because the reaction is in equilibrium, so it doesn't have any sort of voltage that allows the reaction to go in any particular direction. Its in equilibrium and doesn't have the tendency to favor either the reactants or products.
The concentrations of the products and reactants have to not be at equilibrium inorder to generate voltage. If we relate standard cell potential to the equilibrium constant, we get this equation at 25 degrees C: E=(0.0257/n)ln k
Daniel Chen 2L wrote:But doesn't the concentrations of the reactants and products in a concentration cell have to be different in order to generate voltage?
I think in a concentration cell the two electrodes are composed of the same solution, but they differ in concentration so voltage will be generated.
Concentration cells have two cells where the same half-reactions occur, so when calculating the Ecell, the Ecells of each half-reaction would cancel each other out, since they are for the same reaction (except reversed).
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