4 Effect on conditions on cell voltage

Effect of conditions on Cell voltage Ecell The effects of changing conditions on E cell can be made by applying le Chatelier’s principle. Ecell is a measure of how far from equilibrium the cell reaction lies. The more positive the Ecell the more likely the reaction is to occur. If current is allowed to flow, the cell reaction will occur and the Ecell will fall to zero as the reaction proceeds and the reactant concentrations drop. Effect of concentration on Ecell Looking at cell reactions is a straight forward application of le Chatelier. So increasing concentration of ‘reactants’ would increase Ecell and decreasing them would cause Ecell to decrease. Increasing the concentration of Fe2+ and decreasing the concentration of Zn2+ would cause Ecell to increase. Effect of temperature on Ecell Most cells are exothermic in the spontaneous direction so applying Le Chatelier to a temperature rise to these would result in a decrease in Ecell because the equilibrium reactions would shift backwards. If the Ecell positive it indicates a reaction might occur. There is still a possibility, however, that the reaction will not occur or will occur so slowly that effectively it does not happen. If the reaction has a high activation energy the reaction will not occur.