➣ Physical Change: Change in physical properties. Class 12

– Melting

– Boiling

– Condensation

– [Note- No change occurs in the identity of the substance].

➣ Chemical Change:

– Atoms in the reactants are rearranged to form one or more different substances. Class 12

– Old bonds are broken, new bonds are formed.

– Reactants lose their properties to form product of different properties.

4 Fe(s) + 3O2 →2Fe2O3 (rust). Iron Oxygen Ferric oxide

➣ Chemical equation:

The symbolic representation of a chemical reaction is called a

chemical equation.

Features of a chemical equation:

• The reactants are written on the left hand side with a plus sign between them.

• The products are written on the right hand side with a plus sign between them.

• An arrow separates the reactants from the products. The arrow head points towards the

products and indicates the direction of the reaction.

Skeletal chemical equation: A chemical equation which simply represents the symbols and

formulas of reactants and products taking part in the reaction is known as skeletal chemical

equation for a reaction.

For example: For the burning of Magnesium in the air, Mg + O2 → MgO is the skeletal equation.

• Balanced chemical equation: A balanced equation is a chemical equation in which number of

atoms of each element is equal on both sides of the equation i.e number ofatoms of an element on

reactant side = number of atoms of that element on the product side.

➣ Identification:

Combustion : AB + O2 → Oxide of A & B.

Combination : A + B → C

Decomposition : AB → A + B

Displacement : A + BC (aq) → AC (aq) + B

Double

Displacement : AB (aq) + CD (aq) → AD (aq) + CB

Definitions with examples :

1. Combination Reaction :Two or more reactant combine to form a single product.