1st Lecture on Electrochemistry Chemistry Part I12th Standard by Rizwana Mohammed

1. The Malegaon High School & Jr. College
Malegaon, (Nashik), 423203
1st Lecture on Electrochemistry
Chemistry Part I, 12th Science
By
Rizwana Mohammad

2. Electrochemistry
• Dry cell is used to power our electrical and electronic equipment
because it generates electricity.
• Do you know how does a dry cell generate electricity?
• A chemical reaction occurs in it which generates electricity.
• Thus in a dry cell chemical energy is converted into electrical
energy.
• Electrolysis is breaking down of an ionic compound by the passage
of electricity.
• Breaking down of an electrolyte during electrolysis is a chemical
reaction that takes place by the passage of electricity.
• Electrical energy is, thus, converted into chemical energy.
• Electrochemistry deals with the interconversion of chemical and
electrical energy.

3. • It also deals with the resistance and conductance of aqeous
electrolytic solutions.
• The study of electrochemical cells is important in science and
technology.
• Electro-refining, electroplating are also electrochemical processes.
• In an electrochemical cell redox reaction occurs.
Electric conduction:
• The electric current represents a charge transfer.
• A charge transfer or flow of electricity occurs through substances
called conductors.
• There are two types of conductors.
Metallic conduction:
• Conduction by a direct flow of electrons from one point to the
other.
• Metallic conductors are, thus, electronic conductors.

4. Electrolytic or ionic conduction:
• Conduction by the movement of ions of the electrolytes.
• Ionic salts, strong or weak acids and bases are the electrolytes.
• Conduction through electrolytic conductors involves transfer of
matter from one part of the conductor to the other.
Electrical conductance of solution:
According to Ohm's law,
R =
V
I
Unit of electrical resistance is Ohm (Ω). Ω = VA-1
• The electrical conductance, G, of a solution is reciprocal of
resistance
G =
1
R
…1
SI unit of G is siemens (S).
S = Ω-1
S = AV-1
R ∝
l
a
or R = ρ
l
a
…2

5. ρ = proportionality constant is called resistivity of the conductors.
• It is the resistance of conductor of unit length and unit cross
sectional area.
Conductivity (k):
G ∝
a
l
or G = k
a
l
…3
• The proportionality constant k is called conductivity. G = k if length
and cross sectional area of conductor are unity.
• Conductivity is the electrical conductance of unit cube of material.
• Conductivity of solution of an electrolyte is called electrolytic
conductivity which refers to the electrical conductance of unit
volume (1 m3 or 1 cm3) of solution.
G = k
a
l
k = G
𝑙
𝑎
=
1
𝑅
𝑙
𝑎
…4

6. From equation 2 and 4
k =
1
ρ
Units of electrolytic conductivity:
Quantity SI Unit Common Unit
Length m cm
Area m2 cm2
Resistance Ω Ω
Conductivity Ω-1m-1 or Sm-1 Ω-1 cm-1
Molar conductivity: (Λ)
The molar conductivity of an electrolytic solution is the electrolytic
conductivity, k divided by its molar concentration C.
Λ =
𝑘
C
SI unit of molar conductivity is S m2 mol-1.

7. Relation between k and Λ:
Conductivity k is the electrical conductance of 1cm3 of solution. If V is
volume of solution in cm3 containing 1 mole of dissolved electrolyte its
electrical conductance is Λ. Each 1 cm3 portion in the volume V has
conductance k. Hence,
Λ =
𝑘
C
Λ = kV
Concentration of solution = C mol L-1
=
C mol L−1
1000 cm3
L−1 =
C
1000
mol cm-3
V =
1
Concentration
=
1000
C
cm3 mol-1
Λ =
1000𝑘
C