Limitations of the standard cell potentials

We have seen how standard cell potential can be used to predict the feasibility of a redox reaction. However students should also understand the limitations of using the standard cell potentials.

Energetics vs Kinetics
In general, reactions with positive standard cell potentials are energetically feasible. However the standard cell potential does not tell us about the rate of reaction or its kinetic feasibility.

Standard conditions
Standard electrode values are determined under standard conditions such as the concentration of the aqueous metal ion is 1M. Students should not that a concentration of 1M is quite high. In practice, the redox reactions that we are interested in may not have such a high concentration of reacting ions.

Also the standard electrode values vary with the concentration of metal ions. Take for example the reduction of Cu2+. When the concentration of CU2+ is increased beyond 1M, the feasibility of Cu being reduced is increased. Thus the standard electrode potential will become more positive.