Electrochemistry is a branch of chemistry which relates electrical and chemical energies. Electro refers to electricity. In an electrochemical cell, electrical energy is generated using chemical reactions. An electrochemical cell is made by using two beakers having electrolyte in which two electrodes are immersed. The two beakers are connected with a salt bridge. One electrode works as anode and another works as cathode. Anode is related with positive charge and cathode is related with negative charge. Oxidation reaction takes place at anode and reduction reaction takes place at cathode. A continous flow of charge takes place between the two electrodes which gives rise to electricity. Electrons are transferred from anode to cathode and electricity is generated in opposite direction i.e, from cathode to anode. Chemical reactions takes place at both electrodes. The reaction taking place at an individual electrode is called half cell reaction. The two half cell reactions are combined to get overall cell reaction. The overall cell reaction should be balanced. Consider an electrochemical cell having zinc electrode dipped in ZnSO4 electrolyte and copper electrode dipped in CuSO4 electrolyte.
Half cell reaction-
Zn - Zn2+ + 2e (oxidation) Cu2+ + 2e - Cu (reduction)
Overall cell reaction- Zn + Cu2+ - Zn2+ + Cu