Types of Chemical Reactions

Accordingly, the reactions are classified in different types.

1.0Combination Reaction

The reactions in which two or more substances combine to form a single new substance are called combination reactions.

Some more examples of combination reactions  

(a) Between element - element

(i) Burning of Coal

C(s) +  O₂(g) ⎯→ CO₂(g)

Carbon    Oxygen          Carbon dioxide 

(ii) Formation of Water 

2H₂(g)       +                   O₂(g)  ⎯→ 2H₂O()

Hydrogen Oxygen Water

(iii) Burning of Magnesium in air 

2Mg(s) + O₂(g) ⎯→ 2MgO(s)

Magnesium Oxygen Magnesium oxide

(iv) Formation of Iron sulphide

Fe(s) + S(s) ⎯→ FeS(s)

Iron Sulphur                 Iron sulphide

(b) Between compound - compound

(v) Formation of Ammonium chloride

NH₃(g)     + HCl(g) ⎯→ NH₄Cl(s)

Ammonia Hydrogen Ammonium

Chloride Chloride

(vi) Formation of Calcium Carbonate 

CaO(s) + CO₂(g)   ⎯→ CaCO₃(s)

Calcium oxide Carbon Calcium

(Quick lime) dioxide carbonate 

(c) Between compound- element

(vii) Reaction of carbon monoxide with oxygen

2CO(g) + O₂ (g)  ⎯→ 2CO₂(g)

This is also an exothermic reaction.

(viii) 2NO(g) + O₂(g) ⎯→ 2NO₂(g)

2.0Decomposition Reaction

The reaction in which a single compound breaks up into two or more simpler substances is known as decomposition reaction. The decomposition reaction generally takes place when energy in some form such as heat, electricity or light is supplied to the reactants.

Types of Decomposition Reaction 

(a) Thermal decomposition: The reaction in which a single compound breaks up into two or more simpler substances by the action of heat is called thermal decomposition reaction.

(b) Electric Decomposition: The reaction in which a single compound breaks up into two or more simpler substances by the action of electricity is called electric decomposition reaction. 

(c) Photo decomposition: The reaction in which a single compound breaks up into two or more simpler substances by the action of light is called photo decomposition reaction.

Note: Photolysis of AgBr is used in black and white photography.

3.0Displacement Reactions

A reaction in which a more reactive element displaces a less reactive element from its compounds is called displacement reaction. The elements involved may be metals or non-metals.

Relative reactivity of metals

Different metals possess different reactivities. The arrangement of metals in a vertical column in order of their decreasing reactivity from top to bottom is called reactivity series or activity series of metals.

Note : A suggested way of remembering reactivity series

Relative reactivity of some non-metals

Among halogens, fluorine is most reactive, and iodine is least reactive.

F₂ > Cl₂ > Br₂ > I₂

Some more examples of displacement reactions.

(i)Zn(s) + CuSO₄ (aq) ⎯→ ZnSO₄(aq) + Cu(s)

     Zinc           Copper sulphate         Zinc sulphate   Copper

(Bluish-Silver) (Blue)     (Colourless)   (Reddish Brown)

(ii) Cu(s) +    2AgNO₃(aq)  ⎯→ Cu(NO₃)₂(aq)  + 2Ag(s)

      Copper           Silver nitrate Copper nitrate     Silver 

                  (Dark blue)

4.0Double Displacement Reactions 

Those reactions in which two different atoms or groups of atoms are exchanged are called double displacement reactions or double decomposition reactions or metathesis reactions. 

5.0Oxidation and Reduction Reactions

The reaction which involves addition of oxygen or removal of hydrogen from a substance is called oxidation reaction.

The reaction which involves addition of hydrogen or removal of oxygen from a substance is called reduction reaction. 

Note : According to the electronic concept, Oxidation Is Loss of electrons. Reduction Is Gain of electrons.

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