Electrochemistry is a branch of chemistry, which deals with the relationship between electrical energy and chemical changes taking place in redox reactions. i.e., how chemical energy or how electrical energy can be used to bring about a redox reaction which is otherwise not spontaneous. It has many applications in electrolysis, energy producing cell etc.
A variety of definitions exist for electrochemistry. Thus, electrochemistry can be defined "as the science concerned with the mutual transformation of chemical and electrical energy." According to another definition, electrochemistry deals with the structure of electrolyte solutions as well as with the phenomena occurring at the interfaces between metallic electrodes and electrolyte solutions.
By a very general definition adopted is electrochemistry is the science concerned with the physical and chemical properties of ionic conductors as well as with phenomena occurring at the interface between ionic conductors, on the other hand and electronic electronic conductors or semiconductors other ionic conductors and even insulators on the other hand.
Consider a zinc rod being dipped in ZnSO4 solution. The zinc atoms on the surface of the metal with in the solution have tendency to release Zn+2 into solution retaining the electrons on the surface of the metal. This process is called dissolution or solution pressure of the metal and it is oxidative in nature.
The zinc ions of the solution have a tendency to accept the electrons on the surface of zinc rod to form neutral zinc atoms and get deposited on the zinc rod. This process is called deposition or the osmotic pressure of solution is reductive in nature.
These two processes will be taking place simultaneously at different rates. In this case, the rate of dissolution is found to be greater than the rate of deposition. Consequently, by the time equilibrium is reached, more of dissolution would have occurred and the solution becomes negatively charged. Due to the attractive electrostatic forces, the Zn ions accumulate around the Zn rod and an electrical double layer of opposite charges is formed and between the Zn rod and the solution the potential developed is called Zinc Electrode Potential.
Consider a copper rod being dipped in CuSO4 solution. Even in this case, both dissolution and deposition will be taking place simultaneously at different rates. Here, the rate of deposition is found be greater than the rate of dissolution. Hence, by the time the equilibrium is reached, the solution becomes negatively charged while the rod becomes positively charged. Due to the attractive electrostatic forces, the positively charged SO4-2 ions accumulate around the positively charged metal, resulting in the formation of an electrical double layer. The potential developed at the interface is called copper electrode potential.