CBSE Class 12 Chemistry Electrochemistry Notes Set 05

ELECTROCHEMISTRY CONCEPTS 

Electrochemistry may be defined as the branch of chemistry which deals with the quantitative study of interrelation ship between chemical energy and electrical energy and inter-conversion of one form into another.relationships between electrical energy taking place in redox reactions. 

A cell is of two types:- 

I. Galvanic Cell 

II. Electrolytic cell. 

In Galvanic cell the chemical energy of a spontaneous redox reaction is converted into electrical work. 

In Electrolytic cell electrical energy is used to carry out a non-spontaneous redox reaction. 

The Standard Electrode Potential for any electrode dipped in an appropriate solution is defined with respect to standard electrode potential of hydrogen electrode taken as zero. The standard potential of the cell can be obtained by taking the difference of the standard potentials of cathode and anode. 

E⁰_cell = E⁰cathode-E⁰anode 

The standard potential of the cells are related of standard Gibbs energy.

Δ_rG=-nFE⁰_cell 

The standard potential of the cells is related to equilibrium constant. 

Δ_rG= -RTink 

Concentration dependence of the potentials of the electrodes and the cells are given by Nernst equation.
aA+bB ne^--→ cC + dD 

Nernst equation can be written as 

Ecell = E⁰ cell-RT/nF ln[C]^c[D]^d/[A]^a[B]^b 

The conductivity, K of an electrolytic solution depends on the concentration of the electrolyte, nature of solvent and temperature.
Molar Conductivity, Δm, is defined by K/C where C is the concentration in Mol L^-1 ΔM= k*1000/m  

the unit of molar conductivity is Ω ^-1 cm2 mol^-1. Conductivity decrease but molar conductivity increases with decrease in concentration. It increases slowly with decrease in concentration for strong electrolyte while the increase is very dilute solutions. 

Kohlrausch law of independent migration of ions. The law states that limiting conductivity of an electrolyte can be represented as the sum of the individual contribution to the anion and cation of the electrolyte. 

Faraday’s laws of Electrolysis 

I. The amount of chemical reaction which occurs at any electrode during electrolysis by a current is proportional to the quantity of electricity passed through the electrolyte. 

II. The amount of different substances liberated by the same quantity of electricity passing through the electrolytic solution is proportional to their chemical equivalent weights. 

Batteries and full cells are very useful forms of galvanic cells There are mainly two types of batteries. Corrosion of metals is an electrochemical phenomenon In corrosion metal is oxidized by loss of electrons to oxygen and  ormation of oxides.

Anode (Oxidation): 2Fe(s) →2Fe²⁺ + 4e^- 

Cathode (Reduction): O₂(g) + 4H⁺(aq) + 4e^-→2H₂O 

Atmospheric Oxidation: 2Fe²⁺(aq) + 2H₂O(l) + 1/2O₂(g)→Fe₂O₃(s) + 4H⁺(aq) 

QUESTION CARRING 1 MARK 

1. What is the effect of temperature on molar conductivity? 

Ans. Molar conductivity of an electrolyte increases with increase in temperature. 

2. Why is it not possible to measure single electrode potential? 

Ans. (It is not possible to measure single electrode potential because the half cell containing single electrode cannot exist independently, as charge cannot flow on its own in a single electrode.) 

3. Name the factor on which emf of a cell depends:- 

Ans. Emf of a cell depends on following factora. Nature of reactants. 

b. Concentration of solution in two half cells. 

c. Temperature 

d. Pressure of gas. 

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