Science · Class 6
Changes Around Us
Reversible and irreversible changes; expansion and contraction with heat.
4 sections15–25 min read6 MCQs · 2 examples
Chapter Overview
Changes around us can be reversible or irreversible, desirable or undesirable, and physical or chemical. Heating, cooling, mixing, and burning produce different kinds of changes in matter.
Types of Changes
- Reversible: can be undone (ice ↔ water, inflated ↔ deflated balloon)
- Irreversible: cannot be easily undone (burning paper, cooking egg)
- Physical change: no new substance (melting wax, tearing paper)
- Chemical change: new substance formed (rusting, curdling milk)
Causes of Change
- Heating and cooling
- Mixing substances
- Applying pressure
- Exposure to air and moisture (rusting)
Expansion and Contraction
- Metals expand on heating, contract on cooling
- Gaps left in railway tracks for expansion
- Blacksmith heats iron rim before fitting on wooden wheel
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Reversible or not?
Classify: melting ice, burning wood, folding paper.
- 1Melting ice → reversible (refreeze)
- 2Burning wood → irreversible (ash formed)
- 3Folding paper → reversible (unfold)
Answer
Reversible: ice, paper fold | Irreversible: burning wood
Expansion
Why are gaps left between railway tracks?
- 1Rails expand in summer heat
- 2Without gaps, tracks would buckle
- 3Gaps allow safe expansion
Answer
To allow thermal expansion
Key Points to Remember
- ✓ Rusting needs iron, water, and air
- ✓ Chemical changes may show colour change, gas, heat
- ✓ Some changes are both physical and chemical
Exam Tips
- • Give two examples each of reversible and irreversible changes
- • List indicators of chemical change
- • Explain expansion with railway track example
Practice MCQs — Changes Around Us
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Question 1 of 6Score: 0/0
Burning of paper is: