Cell potential or E.M.F of a cell

An electrochemical cell is made up of 2 half cell. One of these act as anode on which oxidation takes place has high electrode potential (Tendency to lose electron) and other electrode or half cell act as cathode on which reduction takes place has lower electrode potential (Tendency to lose electron)

The difference between the potential of two half cell is called cell potential or electro motive force (EMF).

Electro motive force of a cell depends upon (i) Nature of reactant

(ii) Constriction of solution of 2 half cells.

(iii) Temperature

 

 

Electrochemical series:-

It is also called reactivity series in which various element electrodes are arranged in order of their increasing standard reduction potential.

Increasing oxidation potential or Strength of Reducing agent	Li    –     3.05	In left side of S.H.E, on these oxidation takes place Anode Negative charge Have oxidation potential Act as reducing agent
	K    –      2.93
	Na    –    2.71
	Mg   –    2.37
	Al     –    1.66
	Zn    –    0.76
	Fe    –    0.44
	Ni     –   0.25
	Pb    –   0.13
	H      –   0.0
	Cu         0.34	In right side of S.H.E, on These reduction takes place Act as cathode Have positive charge Act as oxidizing agent
	Ag         0.80
	Hg         0.86
	Au         1.50
	F            2.87

 

 

Electrochemical cell made of 2 half cell-

1. Oxidation half cell having oxidation potential.

2. Reduction half cell having reduction potential.

E.M.F of cell or E^o_cell  = Oxidation potential of oxidation half cell + Reduction potential of reduction half cell.

Oxidation potential = -Reduction potential

So E^o_cell  = Reduction potential of oxidation half cell + Reduction potential of reduction half cell

E^o_cell  = Reduction potential of Reduction half cell - Reduction potential of reduction half cell

E^o_cell  = E^o_cathode  - E^o_Anode             

Applications of electrochemical series

1. To compare relative oxidation and reducing power:- Elements with lower reduction potential, can lose electron easily so itself get oxidized and reduce others so called reducing agent.

2. To compare relative activity of metals:-

If metal → Has lower value of reduction potential and metal will be the more reactive

If non-metal→ has higher value of reduction potential and more reactive will be the non-metal

3. To calculate standard EMF of any electrochemical cell:-

E^o_cell  = E^o_cathode  - E^o_Anode     

4. To predict whether a metal reacts with acid to give H₂ gas: - 2M + 2 H⁺ 2 M⁺ + H₂ gas  

5. To predict the spontaneity of a redox reaction:-

 If E^o_cell positive, reaction is spontaneous (Feasible) (Reaction takes places)

E^o_cell negative, reaction is non-spontaneous (non-feasible) (no Reaction)

Cell Representation

X (s)|Xⁿ⁺ (constriction)|| Mⁿ⁺ (constriction)|M (s)

Left side oxidation              salt bridge                Right side reduction

e.g.- Fe + CuSo₄ → Cu + FeSo₄

Fe (s)|Fe²⁺   ||Cu²⁺ (constriction)/Cu (s)