Concentration Cells

[Yen Vuong 2I]

Why is standard potential zero for concentration cells?

[Chem_Mod]

Concentration cells only differ in terms of concentration-- the anode and cathode are made of the same substance. Thus, if you think about it, the anode is just undergoing the reverse reaction of the reaction at the cathode, which means that you are adding a standard potential and its negative value (because you flipped one reaction, you must also flip the sign). Standard potentials do not consider concentration since they are all measured at the same concentration, so the two values just cancel out. A potential difference does exist, but that is calculated using the Nernst equation, which accounts for the differences due to concentration.