Electrochemistry, chapter-3 2021
ELECTROCHEMISTRY
CHAPTER -3
1
, Electrochemistry, chapter-3 2021
• ELECTROCHEMISTRY : It is the study of production of electricity
from energy release during spontaneous chemical reaction and
the use of electrical energy to bring about non-spontaneous
chemical transformation.
• Weak and strong electrolyte : The electrolytes which are ionised
almost completely in aqueous solution are called strong
electrolytes. For eg- H2SO4 , HCl , HNO3 , NaCl etc.
On the other hand, the electrolytes
which ionised to smaller extent are known as weak electrolytes.
For eg- CH3COOH , H3PO4 , Ca(OH)2 etc.
The conducting power is expressed in
terms of degree of ionisation (𝜶). It is also known as degree of
dissociation and may be defined as the ratio of the molecules of
the electrolyte which split into ions to the total number of
molecules of the electrolyte.
𝒏𝒐. 𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒔 𝒐𝒇 𝒆𝒍𝒆𝒄𝒕𝒓𝒐𝒍𝒚𝒕𝒆 𝒘𝒉𝒊𝒄𝒉 𝒔𝒑𝒍𝒊𝒕 𝒊𝒏𝒕𝒐 𝒊𝒐𝒏𝒔
∴𝜶=
𝒕𝒐𝒕𝒂𝒍 𝒏𝒐. 𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒔 𝒐𝒇 𝒕𝒉𝒆 𝒆𝒍𝒆𝒄𝒕𝒓𝒐𝒍𝒚𝒕𝒆
• For strong electrolyte , 𝜶 is almost equal to 1 (𝜶 ≈ 1) since they
are generally completely ionised . But for weak electrolyte 𝜶
h𝒂𝒔 a value smaller than 1 and it depends upon the extent of
their ionisation.
• Electrochemical cell : An electrochemical cell can be defined as a
device in which the redox reaction is carried out indirectly and
the decrease in free energy appears as the electrical energy.This
cell converts the chemical energy liberated during the redox
2
, Electrochemistry, chapter-3 2021
reaction to electrical energy and has an electrical potential equal
to 1.1 volt when the concentration of Zn2+ ion and Cu2+ ion is unit
. Such a device is called galvanic cell.
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
Representation of cell :
Zn(s) | Zn2+(aq) || Cu²+ | cu (s)
Diagram:
• Galvanic cell: A galvanic cell is an electrochemical cell that
converts chemical energy of a spontaneous redox reaction into
electrical energy. Daniel cell is one such cell in which the
following reaction occur:
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
3
, Electrochemistry, chapter-3 2021
This reaction is a combination of two half reactions
whose addition give the overall cell reaction.
Oxidation half reaction :
Zn(s) → Zn2+(aq) + 2e –
Reduction half reaction :
Cu2+(aq) + 2e- → Cu(s)
These reactions occur in two different portions of the Daniel cell.
The reduction half reaction occurs on the Cu-electrode while the
oxidation half reaction occurs on the Zn- electrode. These two
portions of the cell are also called half cell. The Cu-electrode
may be called the reduction half cell and Zn-electrode is called
oxidation half cell .
A potential difference developed between the electrode and
electrolyte which is called electrode potential . When the
concentration of all the species involved in the half cell is unity
then the electrode potential is known as standard electrode
potential . According to IUPAC convention standard reduction
potentials are now called standard electrode potentials . In a
galvanic cell, the half cell in which oxidation takes place is called
anode . It has a negative potential w.r.to the solution . The other
half cell in which the reduction takes place is called cathode . It
has a positive potential w.r.to the solution .
4
ELECTROCHEMISTRY
CHAPTER -3
1
, Electrochemistry, chapter-3 2021
• ELECTROCHEMISTRY : It is the study of production of electricity
from energy release during spontaneous chemical reaction and
the use of electrical energy to bring about non-spontaneous
chemical transformation.
• Weak and strong electrolyte : The electrolytes which are ionised
almost completely in aqueous solution are called strong
electrolytes. For eg- H2SO4 , HCl , HNO3 , NaCl etc.
On the other hand, the electrolytes
which ionised to smaller extent are known as weak electrolytes.
For eg- CH3COOH , H3PO4 , Ca(OH)2 etc.
The conducting power is expressed in
terms of degree of ionisation (𝜶). It is also known as degree of
dissociation and may be defined as the ratio of the molecules of
the electrolyte which split into ions to the total number of
molecules of the electrolyte.
𝒏𝒐. 𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒔 𝒐𝒇 𝒆𝒍𝒆𝒄𝒕𝒓𝒐𝒍𝒚𝒕𝒆 𝒘𝒉𝒊𝒄𝒉 𝒔𝒑𝒍𝒊𝒕 𝒊𝒏𝒕𝒐 𝒊𝒐𝒏𝒔
∴𝜶=
𝒕𝒐𝒕𝒂𝒍 𝒏𝒐. 𝒐𝒇 𝒎𝒐𝒍𝒆𝒄𝒖𝒍𝒆𝒔 𝒐𝒇 𝒕𝒉𝒆 𝒆𝒍𝒆𝒄𝒕𝒓𝒐𝒍𝒚𝒕𝒆
• For strong electrolyte , 𝜶 is almost equal to 1 (𝜶 ≈ 1) since they
are generally completely ionised . But for weak electrolyte 𝜶
h𝒂𝒔 a value smaller than 1 and it depends upon the extent of
their ionisation.
• Electrochemical cell : An electrochemical cell can be defined as a
device in which the redox reaction is carried out indirectly and
the decrease in free energy appears as the electrical energy.This
cell converts the chemical energy liberated during the redox
2
, Electrochemistry, chapter-3 2021
reaction to electrical energy and has an electrical potential equal
to 1.1 volt when the concentration of Zn2+ ion and Cu2+ ion is unit
. Such a device is called galvanic cell.
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
Representation of cell :
Zn(s) | Zn2+(aq) || Cu²+ | cu (s)
Diagram:
• Galvanic cell: A galvanic cell is an electrochemical cell that
converts chemical energy of a spontaneous redox reaction into
electrical energy. Daniel cell is one such cell in which the
following reaction occur:
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
3
, Electrochemistry, chapter-3 2021
This reaction is a combination of two half reactions
whose addition give the overall cell reaction.
Oxidation half reaction :
Zn(s) → Zn2+(aq) + 2e –
Reduction half reaction :
Cu2+(aq) + 2e- → Cu(s)
These reactions occur in two different portions of the Daniel cell.
The reduction half reaction occurs on the Cu-electrode while the
oxidation half reaction occurs on the Zn- electrode. These two
portions of the cell are also called half cell. The Cu-electrode
may be called the reduction half cell and Zn-electrode is called
oxidation half cell .
A potential difference developed between the electrode and
electrolyte which is called electrode potential . When the
concentration of all the species involved in the half cell is unity
then the electrode potential is known as standard electrode
potential . According to IUPAC convention standard reduction
potentials are now called standard electrode potentials . In a
galvanic cell, the half cell in which oxidation takes place is called
anode . It has a negative potential w.r.to the solution . The other
half cell in which the reduction takes place is called cathode . It
has a positive potential w.r.to the solution .
4
