168. What is electrochemical series? What are its important applications?

The table in which the reduction potential of various electrodes has been arranged in the increasing order is called electrochemical series. The standard reduction potential of hydrogen electrode is zero. The electrodes above hydrogen have negative reduction potential while those placed below it have positive reduction potential.

Applications:
(i) To predict the relative oxidising and reducing powers: Greater the reduction potential, more easily the substance is reduced and hence is a stronger oxidising agent. For example oxidising powers of halogens are F₂ > Cl₂ > Br₂ > I₂.

(ii) To predict whether a metal will react with acid to give H₂ gas : Metals above hydrogen in the series displace hydrogen from acids.

(iii) To calculate the standard E.M.F. of the cell


(iv) To predict the spontaneity of any redox reaction: If E.M.F. of the cell is positive, it is spontaneous, otherwise not.