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CHAPTER 7 : REDOX REACTIONS
7.1 Introduction
Practically, all chemical reactions are carried out for
the purpose of generating energy. Combusion of fuels, generation of electricity
by batteries and even metabolism of food are redox (oxidation-reduction)
reactions.
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Oxidation : It is a process in which
a substance (an ion or an atom) loses one or more electrons.
Reduction
: It is a process in which a substance (an ion or an atom)
gains one or more electrons.
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Redox reaction : Electrons are not transferred to
the surroundings in ordinary chemical reactions but electrons lost
by one species, must be gained by another. Such chemical reactions
involving loss of electrons by one species and the simultaneous gain
by another constitute (oxidation - reduction) redox reaction.
Any redox reaction comprises two half reactions: one
corresponding to oxidation and the other to reduction.
Examples
1) 2Ca
+ O2 ®
2CaO Half reaction
2Ca - 4e- ® 2Ca+
2 (Oxidation)
O2
+ 4e- ® 20-
2 (Reduction)
2) Na + 1 Cl2
® NaCl
2
Na - e-
®
Na+ (Oxidation)
1 Cl2
+ e-
® Cl-
(Reduction)
2
A Redox reaction can be represented
as
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