Changes Around Us — Class 6 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 6 Science, Term 2 — Chapter 3. Classifying the changes around us.
1. About this chapter
This chapter covers the different kinds of change — physical/chemical, reversible/irreversible, desirable/undesirable, natural/man-made, and fast/slow.
2. Physical and chemical changes
- A physical change changes only the state, shape or size — no new substance forms. Melting of ice is a change of state; drying of wet clothes in air is a physical change.
- A chemical change forms a new substance — e.g. boiling an egg (an irreversible chemical change).
3. Reversible and irreversible changes
- A reversible change can be undone (melting ice can refreeze).
- An irreversible change cannot be undone — e.g. boiling an egg, the burning of fuel.
4. Other ways to classify changes
| Pair | Examples |
|---|---|
| Desirable / undesirable | the change of seasons is desirable; harmful changes are undesirable |
| Natural / man-made | plants making starch from CO₂ and water is a natural change; acid rain from air pollution is a man-made change |
| Fast / slow | bursting crackers is a fast change; germination of seeds is a slow change |
5. Worked examples
Example 1. What change happens when ice melts? A change in its state (solid to liquid) — a physical change.
Example 2. Is boiling an egg reversible or irreversible? Irreversible (a chemical change).
Example 3. Is acid rain a natural or man-made change? A man-made change.
6. Book-back questions (Samacheer Kalvi)
I. Choose the correct answer
- When ice melts to form water, the change occurs in its — (a) state / (b) mass. Ans: (a) state.
- The drying of wet clothes in air is an example of a — (a) physical change / (b) chemical change. Ans: (a) physical change.
- A desirable change is the — (a) change of seasons / (b) acid rain. Ans: (a) change of seasons.
- Air pollution leading to acid rain is a — (a) natural / (b) man-made change. Ans: (b) man-made change.
II. Fill in the blanks 5. The boiling of an egg results in an irreversible change. 6. Changes that are harmful to us are undesirable. 7. Plants convert carbon dioxide and water into starch — this is a natural change. 8. Bursting of crackers is a fast change, whereas the germination of seeds is a slow change.
III. Answer briefly 9. Differentiate a physical and a chemical change. — A physical change forms no new substance (melting); a chemical change forms a new substance (boiling an egg). 10. Give one example each of a fast and a slow change. — Fast: bursting crackers; slow: germination of seeds.
7. Common mistakes
- Mistake: Calling the melting of ice a chemical change. Fix: Melting is a change of state — a physical change.
- Mistake: Thinking boiling an egg can be undone. Fix: It is an irreversible (chemical) change.
- Mistake: Calling acid rain a natural change. Fix: Acid rain (from pollution) is a man-made change.
8. Quick revision
- Term 2 · Ch 3 · changes around us.
- Physical (no new substance: melting, drying) vs chemical (new substance: boiling an egg).
- Reversible (melting) vs irreversible (boiling egg, burning).
- Also desirable (seasons) / undesirable, natural (starch in plants) / man-made (acid rain), fast (crackers) / slow (germination).
