1. Chemical
Reaction

2. Many changes take place in our surroundings
everyday.

3. Cooking of food, burning of fuel are the
reactions in which substances are totally
transformed. Such transformations are called
chemical changes.

4. The event in which substance gets transformed
permanently (Chemical changes) is called
chemical reaction.

5. The things we use daily are formed because of
chemical reactions.
e.g : The painted walls , things made from plastics

6. To represent chemical reaction they are written
in the form of equation
e.g When Calcium Oxide reacts with water, it produces a
single compound, Calcium hydroxide and energy is
released.
• This reaction is represented in equation form as under.
• CaO + H2O  Ca(OH)2 + energy
Calcium Oxide Water Calcium Hydroxide

7. CaO + H2O  Ca(OH)2
• In a chemical reaction, reactants are written
on left hand side of the arrow whereas
products are written on right hand side of
arrow.
• The substances taking part in a chemical
reaction are called reactants and the
substances formed during the reaction are
called products.

8. Types of Chemical reactions
• Combination reactions
• Reactants two or more than two
• Product only one
• e.g : C + O2  CO2

9. Decomposition reaction
• Reactant only one,
• Products more than one
• e.g : 2H2 0  2H2 + O2

10. Displacement Reaction
• Two or more reactants and products
• One constituent from the reactant displaces
another constituent and separates it to form
the product.
• e.g : Zn + 2HCl  ZnCl2 + H2

11. Oxidation and reduction
• Oxidation- Oxygen combines with an element
or a compound.
e.g : C + O2  CO2
• Reduction - A reaction in which hydrogen
combines with an element or compound or a
reaction in which oxygen is lost from a
compound
Cl2 + H2  2HCl

12. The speed of chemical reactions
Some chemical reactions are fast whereas some
reactions takes place slowly.
e.g : Ripening of fruits, rusting of iron(Slow), Burning of
Paper, Lightening of fire crackers(Fast)

13. Various factors such as the size of the reactant
particles, their temperature and concentration and
the presence of catalysts affect the speed of
reaction.

14. Catalyst doesn’t take part in chemical reaction,
it’s mere presence speeds up a chemical
reaction.
e.g: Manganese dioxide, Raney nickel

15. In some chemical reactions, heat is given out.
(Exothermic Reaction)
e.g : Burning of Magnesium in air.

16. In some chemical reactions heat is absorbed.
(Endothermic reactions)
e.g: dissolving of urea in water
ADD EXPERIMENT

17. Following changes are observed during a
chemical reaction
-Change in the state of the
substance
- Change in temperature
- Change in colour
- Generation of gas