Q. Define standard reduction potential ?

Ans. The standard reduction potential, E^o

As we have seen in the example of a chemical cell in the previous section, the redox reaction "drives" electrons through the circuit. Volts, or voltage, is a measure of the potential for a substance to produce electricity. The tendency for a substance to be reduced is measured by its standard reduction potential, E^o. The more positive the standard reduction potential, the more likely the substance will undergo a reduction reaction.

The following table lists the standard reduction potentials of the commonly used half-cells:

By definition, 2H+ + 2e- -> H₂ is the standard reference cell. The value of its reduction potential Eois zero. All other reduction half-reactions are measured in reference to this value.

In general, the potential of a chemical cell to produce electricity is related to the difference of the half-cell potentials for each of the substances that are involved in the reduction and oxidation half-cells.