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1. Physical and Chemical Changes
Class 8 Science Presentation

2. Physical and Chemical Changes
• - Physical Change: Change in which no new
substance is formed.
• - Chemical Change: Change in which a new
substance is formed.

3. Properties of Physical and
Chemical Changes
• Physical Change:
• - Reversible
• - No new substance formed
• - Change in state, size, or shape
• Chemical Change:
• - Irreversible
• - New substance formed
• - Change in chemical composition

4. Examples of Physical and Chemical
Changes
• Physical Changes:
• - Melting of ice
• - Breaking of glass
• - Dissolving sugar in water
• Chemical Changes:
• - Rusting of iron
• - Burning of wood
• - Cooking of food

5. Difference Between Physical and
Chemical Changes
• Physical Change:
• - No new substance formed
• - Usually reversible
• - Only physical properties change
• Chemical Change:
• - New substance formed
• - Usually irreversible
• - Both physical and chemical properties

6. Rusting of Iron
• - Rusting is a chemical change.
• - Occurs when iron reacts with oxygen and
moisture.
• - Iron + Water + Oxygen → Rust (Iron oxide)
• - Happens in the presence of air and water.

7. Harmful Effects of Rusting
• - Weakens iron objects
• - Reduces strength and durability
• - Causes economic loss
• - Can lead to accidents if structures fail

8. Crystallisation
• - Crystallisation is a physical change.
• - Used to obtain pure solids from solutions.
• - Involves formation of crystals from a
saturated solution.

9. Crystallisation of Copper Sulphate
• - Blue crystals are formed.
• - The process is reversible.
• - Shows purity of the compound.
• - Demonstrates a physical change with a
regular shape.