Spontaneous Reactions

We can use Standard Electrode Potentials to justify why a redox reaction occurs (spontaneous) or does not occur (not spontaneous.

We use the same calculations as we do for electrochemical cells. If the resultant is a positive number, the reaction does occur (spontaneous). If is is less than zero (is negative), then nothing happens.

We can then apply this knowledge to real life situations, such as what happens to a galvanised nail when the zinc coating gets scratched or corroded:

Because the oxidation of zinc, coupled with the reduction of iron, is spontaneous, the compromised section of the nail is protected from further corrosion/damage. Iron ions in the water are actually reduced to iron metal, so "repairing" the scratch/damage.