Physical Changes

• Physical change — form or state changes; no new substance formed.
• Usually reversible — melt ice ↔ freeze water.
• Examples: melting wax, dissolving sugar, breaking glass, crushing chalk.
• Same chemical composition before and after.
• NCERT Chapter 6 — distinguish from chemical changes.
• Size, shape, state changes only.

Level 1 — Core idea

1. Melting — solid → liquid (ice → water); still H₂O.

2. Freezing — reverse of melting.

3. Evaporation — liquid → vapour; salt water → water evaporates, salt remains.

Level 2 — Process and representation

1. Dissolving — sugar in water; sugar particles dispersed, not destroyed.

2. Diagram (text) — cube ice in glass → water at same mass (ignore condensation).

3. Tearing paper — pieces still cellulose; no new chemical.

Level 3 — Applications and NCERT links

1. Real world — making laddu round shape; melting ghee for frying.

2. NCERT Activity — crush chalk, dissolve salt, melt wax — classify.

3. Magnetising iron — physical (intro debate; NCERT lists as physical).

Melting ice and verifying it is physical change

Step 1 — Weigh beaker + ice cubes → mass m₁.
Step 2 — Allow ice to melt at room temperature.
Step 3 — Weigh beaker + water → mass m₂ ≈ m₁ (same substance H₂O).
Step 4 — Freeze water again → ice returns (reversible).
Step 5 — Test with litmus — water neutral before and after.
Step 6 — Compare with burning paper — ash, irreversible, new substances.
Step 7 — Record: no new chemical formed in melting.
Conclusion: melting is physical change — same substance, different state.

• Define physical change.
• Give three examples of physical changes.
• Is melting butter physical or chemical? Why?
• Can physical changes be reversed? Give example.
• Does a new substance form in physical change?
• Is sublimation of iodine physical or chemical?

Open the Practice tab for graded questions on Physical Changes.