Knowledge
Points
1. Oxidation
is defined as a loss of electrons while reduction is defined as a gain of electrons.
2. In a redox reaction, both oxidation
and reduction reaction takes place simultaneously.
3. Direct
redox reaction: In a direct redox
reaction, both oxidation and reduction reactions take place in the same vessel.
Chemical energy is converted to heat
energy in a direct redox reaction.
4. Indirect
redox reaction: In indirect redox
reactions, oxidation and reduction take place in different vessels. In an indirect redox reaction, chemical
energy is converted into electrical energy.
5. In an
indirect redox reaction, the device which converts chemical energy into
electrical energy is known as an electrochemical cell.
6. In an electrochemical cell:
ü The
half cell in which oxidation takes place is known as oxidation half cell.
ü The
half cell in which reduction takes place is known as reduction half cell.
ü Oxidation
takes place at anode which
is negatively charged and reduction takes place at cathode which is
positively charged.
ü Transfer of electrons takes place from anode to
cathode while electric current
flows in the opposite direction.
ü An electrode is made by dipping the metal plate
into the electrolytic solution of
its soluble salt.
ü A
salt bridge is a U shaped tube containing an inert electrolyte in agar-agar and gelatine.
7. A
salt bridge maintains electrical neutrality and allows the flow of electric current by completing the
electrical circuit.
8. Representation
of an electrochemical cell:
ü Anode
is written on the left while the cathode is written on the right.
ü Anode
represents the oxidation half cell and is written as: Metal/Metal ion (Concentration)
ü Cathode
represents the reduction half cell and is written as: Metal ion (Concentration)/Metal
ü Salt
bridge is indicated by placing double vertical lines between the anode and the cathode
ü Electrode
Potential is the potential difference that
develops between the electrode and its electrolyte.
9. When
the concentration of all the species involved in a half cell is unity, then
the electrode potential is known as Standard Electrode Potential. It
is denoted as EΘ.
10. There
are 2 types of electrode potentials: Oxidation potential and reduction potential.
11. Oxidation
potential is the tendency of an electrode to lose electrons or
get oxidized.
12. Reduction
potential is the tendency of an electrode to gain electrons or
get reduced.
13. Oxidation
Potential is the reverse of Reduction Potential.
14. The
electrode having a higher reduction potential has a higher tendency to gain electrons.
So, it acts as a cathode.
15. The
electrode having a lower reduction potential acts as an anode.
16. The
standard electrode potential of an electrode cannot be measured in isolation.
17. According
to convention, the Standard Hydrogen Electrode is taken as a reference electrode and it is assigned a zero
potential at all temperatures.
18. Standard
calomel electrode can also be used as a reference
electrode.
19. Standard
hydrogen electrode. The Standard Hydrogen Electrode can act as
both anode and cathode.
If the
standard hydrogen electrode acts as an anode: H2 (g) → 2H+
(aq) + 2e-
If the
standard hydrogen electrode acts as a cathode: 2H+ (aq) + 2e-→
H2 (g)
20. In the electrochemical series,
various elements are arranged as per their standard reduction potential values.
21. A
substance with higher reduction potential value means that it has a higher tendency to get reduced.
So, it acts as a good oxidising agent.
22. A
substance with lower reduction potential value means that it has a higher tendency to get oxidised.
So, it acts as a good reducing agent.
23. The
cell potential is the difference between the
reduction potential of cathode and anode. E cell = E cathode – E anode
Cell potential is called the electromotive
force of the cell (EMF) when no current is drawn through the cell.
24. Nernst
studied the variation of electrode potential of an electrode with temperature and concentration of electrolyte.
25. Nernst
formulated a relationship between standard electrode potential EÓ©
and electrode potential E.
26. Electrode
potential increases with increase in the
concentration of the electrolyte and decrease in temperature.
27. Nernst
equation when applied to a cell:
This helps in calculating the cell potential
28. At
equilibrium, cell potential Ecell becomes zero.
29. Relationship
between equilibrium constant Kc and standard cell potential EÓ©cell:
30.
Work done by an
electrochemical cell is equal to the decrease in Gibbs energy
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