Changes Around Us (NCERT Ch. 6)

• Distinguish between reversible changes (can be undone) and irreversible changes (cannot be undone).
• Identify changes caused by heating/cooling, and changes that are slow vs fast.
• Relate everyday examples (melting ice, cooking food, stretching a rubber band, burning paper) to these categories.

1. A reversible change can be reversed to get back the original substance/state (e.g. melting ice can be refrozen).
2. An irreversible change cannot easily be undone to get the original substance back (e.g. burning paper, cooking an egg).
3. Changes can also be classified by speed: fast changes (e.g. bursting a balloon) vs slow changes (e.g. rusting of iron, growth of a plant).
4. Heating can cause reversible changes (melting wax) or irreversible changes (burning wood).

Is stretching a rubber band a reversible or irreversible change?

When released, the rubber band returns to its original shape and size.
This is a reversible change.

• Assuming all heating causes irreversible change (melting ice/wax by heat IS reversible on cooling).
• Confusing "slow" changes with "irreversible" changes — they are independent categories (rusting is both slow AND irreversible, but not all slow changes are irreversible).
• Thinking burning paper can somehow be reversed by adding more paper — the original substance is permanently changed to ash and gases.

• Is melting of ice reversible or irreversible?
• Is cooking a raw egg reversible or irreversible?

Open the Practice tab for graded questions on Changes Around Us (NCERT Ch. 6).