CBSE Class 10 Answered

Substitution reaction:

• The reaction in which one or more hydrogen atoms of a hydrocarbon are replaced by some other atoms is called a substitution reaction.
• Substitutions reactions are a characteristic property of saturated hydrocarbons (Alkanes).
• For example: Methane reacts with chlorine in the presence of sunlight to form     chloromethane and hydrogen chloride.

Where, R is an alkyl group.

Addition reaction:

• The reaction which involves direct addition of an attacking agent, across the double or triple bonds are called addition reactions.
• An unsaturated hydrocarbon combines with another substance to give a single product.
• Addition reaction like the addition of hydrogen, chlorine or bromine are a characteristic property of unsaturated hydrocarbons.
• This reaction occurs only in unsaturated compounds where there are double or triple bonds.

e.g.

Combustion Reaction:

• Combustion or Burning is a chemical change in which combustible substances combine with oxygen to produce new products called oxides with the liberation of heat and light.
• It is an exothermic reaction.

For example combustion of methane is given as under

CH₄ + 2O₂ →  CO₂ + 2H₂O

Magnesium combines with oxygen to form white colour magnesium oxide with liberation of some amount of heat.