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CLASS 7-Physical and Chemical changes

Physical and Chemical changes


·         A change is called physical change when a substance undergoes a change in its physical properties such as shape , size, color & state of matter. and .

·         Properties such as shape, size, colour, and state of substance are called physical properties.

·         A physical change is generally reversible

·         In physical change where no new substance are formed.

·         The chemical properties of the substance doesn’t change.


·         A change is called chemical change when a substance undergoes a change in its chemical propertiesand form a new substance .

·         The chemical change is irreversible.

·          During chemical change heat, light, sound or gas may produce.

·         A change in colour or smell may occur.

·         Example :- Burning  of magnesium ribbon, Changing milk into curd, Ripening of fruits.

 Burning of magnesium ribbon:-

Magnesium (Mg) + Oxygen (O2)  Magnesium oxide (MgO)

Magnesium oxide (MgO) + Water (H2O)  Magnesium hydroxide [Mg(OH)2]



·         The chemical formula for rust is Fe2O3 and is commonly called ferric oxide or iron oxide.

·         Rusting is harmful since the object made of iron like gates, pillars, chains, bridges etc. get rusted which results in eating away the metal which finally gets converted into powder.

·         To prevent rusting paint is applied on the surface of iron.

·         By galvanization (zinc coat) rusting can be prevented.


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