Electrochemical Cell

Electrochemical cell :-

• An electrochemical cell is a device that converts the chemical energy into electrical energy of a spontaneous redox reaction. (Definition ) 
• Here Gibbs free energy of the spontaneous redox reaction is converted into electrical work which may be used for running a motor or other electrical gadgets like geyser, fan , heater etc 
•  Electrochemical or Voltaic(galvanic) cells are of a type that produce electric current as a result of chemical reaction 
• Apparatus:- Electrochemical cell consists of -Two electrodes usually set up in two separate beakers. The electrolytes taken in the two beakers are different. The electrodes taken are of different materials. To set up this cell , a salt bridge/porous pot is used. 
• Sign Convention :- Anode (-ve pole) & cathode(+ve pole) 
• Cell Diagram :- 
  

  salt Bridge :- Necessity to use salt bridge 

• It is a U-shaped tube that contains a gel permeated with a solution of an inert electrolyte such as Sodium sulphate, potassium nitrate or potassium sulphate etc  . The ions of the inert electrolyte do not react with the other ions in the solution & they are not oxidised or reduced at the electrodes. The salt-bridge is necessary to complete the electrical circuit & to maintain electrical neutrality in both compartments ( by flow of ions) 

                                Representation of Electrochemical cell 

Chemical reaction involved in electrochemical cell

Facts :- 

1. If the external potential applied becomes greater than internal one then cell behaves as an electrolytic cell & thus the direction of flow of current is reversed 
2. The potential difference between the two electrodes of a galvanic cell is called cell potential & is measured in Volts.It is called emf of the cell when no current is drawn through the cell.
3. For Daniell cell, the cell potential is -1.1V . 
4. Ecell= Eright - E left
5. Measurement of electrode potential is done by using SHE( standard Hydrogen Electrode)