Chapter- 3 Electrochemistry
Introduction
It is the branch of chemistry, which deal with interconversion of electrical and chemical energy, the
behavior of electrolytes and the equilibrium in electrolytes.
Chemical energy ⇌ electrical energy
Basic terms of electrochemistry
Metallic conductors: Substances which allow the electric current to pass through them in their solid
state :
Eg : Metals, Graphite.
Insulators: Substances which do not allow the electric current in their solid state.
Eg : Glass, rubber, wood etc.
Electrolytic conductors: Chemical substances which allow the electric current to pass through them
either in the molten state or in the aqueous state.
Eg :NaCl(aq).HCl(aq) H2SO4(aq) etc.
Electrolytic conductors are also called Ionic conductors.
Comparison between metallic and electrolytic conductor
Metallic Conductors Electrolytic conductors
i) They conduct electricity in solid state. They conduct electricity either in molten or in
aqueous state.
ii) Free or valence electrons are charge carriers. Free ions are charge carriers
iii) They do not undergo any change in chemical Undergo change in chemical composition
composition
iv)Conductivity decreases with increase of Conductivity increases with increase of temperature
temperature
Non-Electrolytes
Chemical substances which do not allow the electric current to pass through them either in molten or
aqueous state.
Eg: Sugar solution Glucose, Benzene, Urea, Toluene etc.
Difference between electrolytes and non-electrolytes :
Electrolytes Non Electrolytes
(i) Electrolytes conducts electricity either in They do not conduct electricity either in molten or in
molten state or in aqueous state. aqueous state.
(ii) They undergo dissociation in water to form They do not undergo dissociationC12H22O11(aq)→ No
free ions. NaCl (aq) ® Na +
(aq) + Cl-
(aq) ions.
iii) They are usually ionic or polar covalent They are generally non polar covalent compounds.
compounds.
Eg: NaCl, KNO3, HCl, H2SO4, NaOH, KOH etc eg: Sucrose, Glucose, ethanol, Benzene etc.
,Classification of Electrolytes
Based on the extent of degree of dissociation in aqueous solution, they are classified into two types:
i) Strong Electrolytes:
Chemical compounds which denouatis completely into ions
eg: Strong acids: HCl, HNO3, H2SO4 etc.
Strong bases : KOH, NaOH, Ba(OH)2 etc.
Salts :NaCl, KCl, KNO3, NH4NO3 etc.
Properties of strong eleectrolytes :
Strong electrolytes undergo complete dissociation even in small amount of water concentrated solution.
As strong electrolytes undergo complete dissociation, further dilution will not affect the dissociation.
Conductance of strong electrolyte in a solution almost remains same or increases by a very small value
on dilution.
ii)Weak Electrolytes :
Compoundswhich undergo partial dissociation in water and produces small quantity of ions. The
dissociation of weak electrolyte increases with dilution.
eg: Weak acids : HCOOH, CH3COOH, H2C2O4, HCN, H3PO3, H2S, H2CO3 etc.
Weak Bases : NH4OH, Mg(OH)2, amines; CH3 NH2, C2H5NH2, C6H5NH2.
Properties of weak electrolytes
The dissociation of weak electrolytes in concentrated solution is very less and it increases with increase
of dilution.
The dissociation will be complete under infinite dilution & it can behave as strong electrolyte.
Conductance of weak electrolyte in concentrated state is less and increases with dilution as the
dissociation increases with dilution. Under infinite dilution state weak electrolyte contain more number
of ions.
Degree of dissociation ( )
It is defined as the fraction of total number of molecules of the electrolytes which ionizes or dissociates
in the solution. It is represented by Alpha ().
Number of moles of electrolyte undergoing dissociation
=
Total number of moles of electolytes
Degree of dissociation is used to express the extent of dissociation of weak electrolyte.
Suppose an electrolyte dissociate to an extent of 40 percent, then the degree of dissociation () is
40
a = = 0.4
100
, Note
1. For strong electrolytes is almost equal to 1
2. For weak electrolytes is always less than 1.
In electrochemistry there are two processes:
(i)Electrochemical process – is a process where chemical energy (chemical reaction) is converted into
electrical energy(electricity). eg: Mobile phone batteries, car battery etc.
(ii) Electrolytic process- is a process where electrical energy (electricity) induces /starts chemical
reaction. eg:- Battery when charged.
Cell /Battery-is a device where interconversion of electrical and chemical energies take place.
Cells can be classified into 2 types
(i) Electrochemical cell: is a device where chemical energy is converted into electrical energy.
eg: Mobile phone batteries.
(ii) Electrolytic cell- is a device where electrical energy is converted into chemical energy.
eg: Cell used during electrolytic refining of copper
Cathode
Electrolytic cell
Anode
HCl→ H+ + Cl−(ionization).
At anode: (oxidation).
HCl
2Cl−→ Cl2 +2e−
(aq)
At cathode (−): (Reduction)
2H+ +2e−→H2
Electrochemical cells or Galvanic Cells
An electrochemical is the device or the set up in which the electrical energy is produced from the
spontaneous chemical reactions. (red- Ox-reactions)
eg: Galvanic cell or Daniel cell.
In the galvanic cells reduction and oxidation reactions occur in two different beakers called as half cells.
Introduction
It is the branch of chemistry, which deal with interconversion of electrical and chemical energy, the
behavior of electrolytes and the equilibrium in electrolytes.
Chemical energy ⇌ electrical energy
Basic terms of electrochemistry
Metallic conductors: Substances which allow the electric current to pass through them in their solid
state :
Eg : Metals, Graphite.
Insulators: Substances which do not allow the electric current in their solid state.
Eg : Glass, rubber, wood etc.
Electrolytic conductors: Chemical substances which allow the electric current to pass through them
either in the molten state or in the aqueous state.
Eg :NaCl(aq).HCl(aq) H2SO4(aq) etc.
Electrolytic conductors are also called Ionic conductors.
Comparison between metallic and electrolytic conductor
Metallic Conductors Electrolytic conductors
i) They conduct electricity in solid state. They conduct electricity either in molten or in
aqueous state.
ii) Free or valence electrons are charge carriers. Free ions are charge carriers
iii) They do not undergo any change in chemical Undergo change in chemical composition
composition
iv)Conductivity decreases with increase of Conductivity increases with increase of temperature
temperature
Non-Electrolytes
Chemical substances which do not allow the electric current to pass through them either in molten or
aqueous state.
Eg: Sugar solution Glucose, Benzene, Urea, Toluene etc.
Difference between electrolytes and non-electrolytes :
Electrolytes Non Electrolytes
(i) Electrolytes conducts electricity either in They do not conduct electricity either in molten or in
molten state or in aqueous state. aqueous state.
(ii) They undergo dissociation in water to form They do not undergo dissociationC12H22O11(aq)→ No
free ions. NaCl (aq) ® Na +
(aq) + Cl-
(aq) ions.
iii) They are usually ionic or polar covalent They are generally non polar covalent compounds.
compounds.
Eg: NaCl, KNO3, HCl, H2SO4, NaOH, KOH etc eg: Sucrose, Glucose, ethanol, Benzene etc.
,Classification of Electrolytes
Based on the extent of degree of dissociation in aqueous solution, they are classified into two types:
i) Strong Electrolytes:
Chemical compounds which denouatis completely into ions
eg: Strong acids: HCl, HNO3, H2SO4 etc.
Strong bases : KOH, NaOH, Ba(OH)2 etc.
Salts :NaCl, KCl, KNO3, NH4NO3 etc.
Properties of strong eleectrolytes :
Strong electrolytes undergo complete dissociation even in small amount of water concentrated solution.
As strong electrolytes undergo complete dissociation, further dilution will not affect the dissociation.
Conductance of strong electrolyte in a solution almost remains same or increases by a very small value
on dilution.
ii)Weak Electrolytes :
Compoundswhich undergo partial dissociation in water and produces small quantity of ions. The
dissociation of weak electrolyte increases with dilution.
eg: Weak acids : HCOOH, CH3COOH, H2C2O4, HCN, H3PO3, H2S, H2CO3 etc.
Weak Bases : NH4OH, Mg(OH)2, amines; CH3 NH2, C2H5NH2, C6H5NH2.
Properties of weak electrolytes
The dissociation of weak electrolytes in concentrated solution is very less and it increases with increase
of dilution.
The dissociation will be complete under infinite dilution & it can behave as strong electrolyte.
Conductance of weak electrolyte in concentrated state is less and increases with dilution as the
dissociation increases with dilution. Under infinite dilution state weak electrolyte contain more number
of ions.
Degree of dissociation ( )
It is defined as the fraction of total number of molecules of the electrolytes which ionizes or dissociates
in the solution. It is represented by Alpha ().
Number of moles of electrolyte undergoing dissociation
=
Total number of moles of electolytes
Degree of dissociation is used to express the extent of dissociation of weak electrolyte.
Suppose an electrolyte dissociate to an extent of 40 percent, then the degree of dissociation () is
40
a = = 0.4
100
, Note
1. For strong electrolytes is almost equal to 1
2. For weak electrolytes is always less than 1.
In electrochemistry there are two processes:
(i)Electrochemical process – is a process where chemical energy (chemical reaction) is converted into
electrical energy(electricity). eg: Mobile phone batteries, car battery etc.
(ii) Electrolytic process- is a process where electrical energy (electricity) induces /starts chemical
reaction. eg:- Battery when charged.
Cell /Battery-is a device where interconversion of electrical and chemical energies take place.
Cells can be classified into 2 types
(i) Electrochemical cell: is a device where chemical energy is converted into electrical energy.
eg: Mobile phone batteries.
(ii) Electrolytic cell- is a device where electrical energy is converted into chemical energy.
eg: Cell used during electrolytic refining of copper
Cathode
Electrolytic cell
Anode
HCl→ H+ + Cl−(ionization).
At anode: (oxidation).
HCl
2Cl−→ Cl2 +2e−
(aq)
At cathode (−): (Reduction)
2H+ +2e−→H2
Electrochemical cells or Galvanic Cells
An electrochemical is the device or the set up in which the electrical energy is produced from the
spontaneous chemical reactions. (red- Ox-reactions)
eg: Galvanic cell or Daniel cell.
In the galvanic cells reduction and oxidation reactions occur in two different beakers called as half cells.
