Electrochemical Cells:

An electrochemical cell consists of two metallic electrodes immersed in either the same electrolyte solution or in two different solutions that are in electrolytic contact. An electrochemical cell can operate to convert chemical energy into electrical energy or vice-versa depending on whether the cell reaction is spontaneous or force to occur in the non-spontaneous direction.

The cell in which the electrode reaction occurs spontaneously when the electrodes are externally connected by a conductor and it serves as a means of converting chemical energy into electrical energy is called the Galvanic cell or voltaic cell.  Alternatively, the cell in which the cell reaction is force to occur in the non-spontaneous direction by passing the current through the cell from an external source to affect a chemical transformation is called the electrolytic cell.  A little confusion is possible if we attempt to discuss both types at once. Thus, we will confine our attention within this unit to galvanic cells.  Discussion of the electrolysis cell will be made elsewhere.