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Posted: Sun Feb 18, 2018 7:31 pm
How does concentration affect cell potential?
Posted: Sun Feb 18, 2018 8:04 pm
Since the Nernst Equation is as follows: E=E°-(RT/nF) ln Q, we can see that the cell potential (E) depends on the value of Q, which is the concentration of the products over the concentration of the reactants.
Posted: Sun Feb 18, 2018 8:20 pm
the higher the concentration of products, the higher the value of Q, the more negative the value of Ecell, and therefore the reaction it is un-spontaneous
the higher the concentration of reactants, the lower the value of Q, the more positive the value of Ecell, and therefore the reaction is spontaneous
Posted: Sun Feb 18, 2018 10:30 pm
Think of it just like how we looked at Q and K in Chem 14A. The only addition in electrochem is that we look at cell potential as well, which is related to Q. As the reaction proceeds, concentrations of reactants decrease and that of products increases. This makes a larger Q and when Q is large enough to equal K, the reaction is at equilibrium. At equilibrium no net change is occurring and dG=0 meaning no energy is free to do work. Therefore, the ability of the cell to do work, the cell potential, is also 0. If concentration of reactants is high, the forward reaction is favored, so a current will be generated as the reaction proceeds. The higher the concentration of reactants in relation to products, the greater the cell potential (for concentration cells).