Biochemistry

1. “Different Types
of Chemical
Reactions”
Dr. Kalim Ullah
Post RN Semester-I,
Biochemistry
Unit-4
1
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2. Different types of chemical reaction 2
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3. In a chemical reaction, the substances which react together
are called reactants whereas the new substances formed are
called products.
• The change of one or more substances into
other substances having different composition
and properties is called a chemical reaction.
C(s) + O2(g) CO2(g)
2H2(g) + O2(g) 2H2O(g)
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Example:

4. Combination reactions
Decomposition reactions
Displacement reactions
Double-displacement reactions
Oxidation-reduction reactions
Precipitation reactions
Exothermic and endothermic reactions
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5.  What is combination reaction?
• A reaction in which two or more substances (elements or compounds)
combine together to form a new substance is called a combination
reaction.
• Many combustion reaction are also examples of combination reaction.
where A,B,C and ABC represent elements or compounds
A B C A B C
+ +
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6. • Examples:
• H2(g) + Cl2(g) 2HCl(l)
• Mg(s) + Cl2(g) MgCl2(s)
• Fe(s) + S(s) FeS (s)
• MgO(s) + H2O(l) Mg(OH)2 (aq)
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7. Synthesis Reaction:
» The combination reaction in which a compound is formed
from its constituent elements is called “synthesis reaction”.
Example:
 Synthesis of ammonia (NH3)
N2(g) + 3H2(g) 2NH3(g)
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8. What is decomposition reaction?
• A reaction in which a substance is broken down
into two or more simpler substances is known as
decomposition reaction.
• A decomposition reaction is opposite of
combination. A decomposition reaction takes
place only when some energy in form of heat,
light or electricity is supplied to the reactant.
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9. Various types of decomposition reactions
1. Thermal decomposition reaction
o Decomposition caused by heating
2. Electrolytic decomposition (electrolysis) reaction
o Decomposition reaction caused by electricity
3. Photodecomposition reaction
o Decomposition reaction caused by light
A B C A B C
+ +
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where A,B,C and ABC represent an element or compound .

10. • Examples:
• ZnCO3(g) ZnO(s) + CO2(g)
• 2H2O (l) 2H2(g) + O2(g)
• CaCO3(s) CaO (s) + CO2 (g)
• 2H2O2(l) 2H2O(l) + O2(g)
electrolysis
UV
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11. What is displacement reaction?
• A reaction in which one part (an atom or a
group of atoms) of a molecule is replaced by
another is called a displacement reaction.
Y Z
+
X X Z
Y +
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where X,Y,Z represent an element or compound .

12. • Examples:
• Zn(s) + 2HCl(dil) ZnCl2(aq) + H2(g)
• 2KBr(aq) + Cl2(aq) 2KCl(aq) + Br2(aq)
• CuSO4(aq) + Zn(s) Cu(s) + ZnSO4(aq)
• Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)
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13. What is double-displacement reaction?
• A reaction in which the two reacting ionic
compounds exchange their corresponding ions
is called a double-displacement reaction.
Z
+
X X Z
Y +
W W
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Y
where W,X,Y,Z represent an element or compound .

14. • Examples:
• AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
• Ni(NO3)2 (aq) + 2NaOH (aq) Ni(OH)2(s) + NaNO3(aq)
• 2KBr(aq) + BaI2 (aq) 2KI(aq) + BaBr(aq)
• Pb(CH3COOH)2(aq) +2HCl(aq) PbCl2(s) + CH3COOH(aq)
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precipitate
precipitate

15. Oxidation occurs when a molecule
does any of the following:
Loses electrons
Loses hydrogen
Gains oxygen
Increase in oxidation number (Valency)
If a molecule undergoes oxidation, it has
been oxidized and it is the reducing agent

16. Reduction occurs when a molecule does any of the
following:
Gains electrons
Gains hydrogen
Loses oxygen
Decrease in oxidation number
If a molecule undergoes reduction,
it has been reduced and it is the
oxidizing agent.

17. Oxidation Reduction Chemisty: Redox Chemistry
Oxidation and Reduction reactions always take
place simultaneously.
Loss of electrons – oxidation (Increase in Oxidation Number)
Ex:Na ------> Na+1 + e-1
Gain of electrons - reduction ( Decrease in Oxidation Number)
Cl2 + 2 e-1 ------> 2 Cl-1

18. Follow the electrons

19. Different types of chemical reaction 19
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21. zinc is being oxidized while the copper is
being reduced. Why?

22. Redox reactions involve electron transfer:
Lose e - =Oxidation
Cu (s) + 2 Ag + (aq) Cu 2+ (aq) + 2 Ag(s)
Gain e - =Reduction

23. Identifying OX, RD, SI
Species
• Ca0 + 2 H+1Cl-1  Ca+2Cl-1
2 + H2
0
• Oxidation = loss of electrons. The species becomes more
positive in charge. For example, Ca0  Ca+2, so Ca0 is the
species that is oxidized.
• Reduction = gain of electrons. The species becomes more
negative in charge. For example, H+1  H0, so the H+1 is
the species that is reduced.
• Spectator Ion = no change in charge. The species does not
gain or lose any electrons. For example, Cl-1  Cl-1, so the
Cl-1 is the spectator ion.

24. What do you mean by oxidation-reduction reaction?
• Oxidation reaction: any process involving addition
of oxygen, removal of hydrogen and/or loss of
electron is known as oxidation reaction.
• Example:
Addition of oxygen
• P4(s) + 5O2(g) 2P2O5(s) (oxidation of P4)
Removal of hydrogen
• H2S(aq) + Br2(aq) 2HBr(aq) + S(s) (oxidation of H2S)
Loss of electron
• Al (s) Al3+(aq) + 3e- (oxidation of Al)
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25. • Oxidising agent : The substance which brings about oxidation of other
substances is called an oxidising agent.
 Example: 1. KMnO4 (potassium permanganate)
2 .H2SO4 (conc. sulphuric acid)
• Reduction reaction: any process involving removal of oxygen, addition
of hydrogen and/or gain of electron is known as reduction reaction.
• Example:
Removal of oxygen
Fe2O3(s) + 3CO(g) Fe(s) + 3CO2(g) (reduction of Fe2O3)
Addition of hydrogen
H2S(aq) + Cl2(g) 2HCl(aq) + S(s) (reduction of Cl)
Gain of electron
Cu2+(aq) + 2e- Cu(s) (reduction of Cu2+)
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26. • Reducing agent: The substance which brings about
reduction of other substance is called a reducing
agent.
 Example: 1. H2 (hydrogen)
2.SO2 (sulphur dioxide)
“Reduction is the reverse of oxidation”
“Oxidation and reduction are mutually dependent, i.e. oxidation
and reduction are reciprocal. Thus, in a reaction if a substance
oxidises, another reduces.”
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27. What is precipitation reaction?
• The reaction in which one of the products formed
is an insoluble substance and is thrown out of the
solution as a solid (called precipitate) is called
precipitation reaction.
• The formed precipitate is indicated by a downward
arrow( ).
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28. • Examples:
• AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)
• Pb(NO3)2 (aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)
• BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq)
• LiBr(aq) + AgNO3(aq) LiNO3(aq) + AgBr(s)
precipitate
precipitate
precipitate
precipitate
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29.  What do you mean by exothermic and endothermic reaction?
• Reaction which is accompanied by evolution of heat is known as
exothermic reaction whereas reaction accompanied by absorption of
heat is known as endothermic reaction.
 Melting of ice is an endothermic reaction
 Freezing of water is an exothermic reaction
 Exothermic and endothermic are reverse of each other.
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Reactants Product
endothermic
exothermic

30. • Example:
• H2O(s) + heat H2O(l) (endothermic)
• C(s) + H2O(v) + heat CO(g) + H2(g) (endothermic)
• CH4(g) + 2O2(g) CO2(g) + 2H2O(g) + heat (exothermic)
• H2(g) + O2(g) H2O(g) + heat (exothermic)
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Endothermic
reaction
Exothermic
reaction

31. Different types of chemical reaction/The End 31
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