6 Effects of conditions on cell emf

Effect of conditions on cell e.m.f The effects of changing conditions on cell e.m.f can be made by applying le chateliers principle E.m.f. is a measure of how far from equilibrium the cell reaction lies. The more positive the e.m.f the more likely the reaction is to occur. If current is allowed to flow, the cell reaction will occur and the emf will fall to zero as the reaction proceeds and the reactant concentrations drop Effect of concentration on cell e.m.f Looking at cell reaction is a straight forward application of le chatelier. So increasing concentration of ‘reactants’ would increase EMF and decreasing them would cause EMF to decrease Increasing the concentration of Fe2+ and decreasing the concentration of Zn2+ would cause Ecell to increase Effect of temperature on cell e.m.f Most Ecells are exothermic in the spontaneous direction so applying Le chatelier to a temperature rise to these would result in a decrease in Ecell. Zn2+(aq) + 2e-
Zn(s) E= – 0.76V Fe2+(aq) + 2e-
Fe(s) E= -0.44V Zn + Fe2+
Fe + Zn2+ E= +0.32. 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 doesn’t happen. If the reaction has a high activation energy the reaction will not occur.