Complete Notes for Class 7, 8, 9, 10, NTSE, Olympiad, NEET & JEE Foundation
1. What is a Change?
Any alteration in shape, size, state, position, colour, composition, or properties of a substance is called a change.
Physical Change → Only physical properties change
Chemical Change → New substance with different chemical properties is formed
Chemical Change → New substance with different chemical properties is formed
2. Physical vs Chemical Change – Master Table
| Point of Difference | Physical Change | Chemical Change |
|---|---|---|
| Nature | Temporary & reversible | Permanent & usually irreversible |
| New substance formed? | No | Yes |
| Composition | No change in chemical composition | Composition changes |
| Energy change | Very little or none | Large energy change (heat, light, sound) |
| Mass | No change in total mass | No change in total mass (Law of conservation) |
| Examples | Melting ice, boiling water, tearing paper | Burning paper, rusting iron, digestion of food |
3. Physical Changes – Detailed
Definition: A change in which no new substance is formed and the change is generally reversible.
Common Types & Examples
| Type | Examples |
|---|---|
| Change of State | Ice → Water → Steam Glowing of bulb |
| Change of Shape/Size | Making toys from clay Cutting vegetables |
| Dissolving | Sugar dissolves in water Salt in water |
| Magnetisation/Demagnetisation | Making magnet from iron |
| Sublimation | Naphthalene balls disappear |
Trick: If you can get the original substance back easily → Physical change!
4. Chemical Changes – Detailed
Definition: A change in which one or more new substances with different properties are formed. Also called chemical reaction.
Signs of Chemical Change (Very Important for Exams)
- Evolution of gas → Bubbles (e.g., baking soda + vinegar → CO₂)
- Change in colour → Apple turns brown, copper turns green
- Change in temperature → Burning (heat released), slaked lime (heat released)
- Formation of precipitate → Cloudy appearance
- Evolution of light/smell → Burning of cracker, rotten egg smell
Common Examples
| Process | Chemical Change | New Substance Formed |
|---|---|---|
| Burning of wood/paper | Yes | Ash, CO₂, smoke |
| Rusting of iron | Yes | Rust (Fe₂O₃·xH₂O) |
| Digestion of food | Yes | Glucose, amino acids |
| Cooking food | Yes | New compounds |
| Photosynthesis | Yes | Glucose + O₂ |
| Respiration | Yes | CO₂ + H₂O + energy |
| Burning of candle | Both! | Wax melting = Physical Wax burning = Chemical |
5. Tricky Examples (Most Asked in Exams)
Q. Burning of candle → Both physical & chemical
→ Melting of wax = Physical
→ Burning of wax vapour = Chemical (produces CO₂ & H₂O)
→ Melting of wax = Physical
→ Burning of wax vapour = Chemical (produces CO₂ & H₂O)
Q. Crystallisation of salt from seawater → Physical change
→ Only water evaporates, salt remains same
→ Only water evaporates, salt remains same
Q. Bursting of crackers → Chemical change
→ Light, sound, heat, new gases formed
→ Light, sound, heat, new gases formed
Q. Glowing of bulb → Physical change
→ Only electrical energy → heat & light (no new substance)
→ Only electrical energy → heat & light (no new substance)
50 Practice MCQs with Answers & Explanations
1. Burning of magnesium ribbon in air is a:
A) Physical change B) Chemical change C) Both D) None
B) Chemical change
A) Physical change B) Chemical change C) Both D) None
B) Chemical change
Mg + O₂ → MgO (new substance formed with bright light).
2. Melting of ice is a:
A) Chemical change B) Physical change C) Irreversible change D) Nuclear change
B) Physical change
A) Chemical change B) Physical change C) Irreversible change D) Nuclear change
B) Physical change
Only state changes; water can be frozen again.
3. Which is NOT a sign of chemical change?
A) Evolution of gas B) Change in colour C) Change in temperature D) Change in state
D) Change in state
A) Evolution of gas B) Change in colour C) Change in temperature D) Change in state
D) Change in state
Change in state alone is usually physical.
4. Burning of a candle involves:
A) Only physical change B) Only chemical change C) Both D) Neither
C) Both
A) Only physical change B) Only chemical change C) Both D) Neither
C) Both
Melting of wax → physical; burning of wax → chemical.
5. Rusting of iron is:
A) Physical change B) Chemical change C) Reversible D) Desirable change
B) Chemical change
A) Physical change B) Chemical change C) Reversible D) Desirable change
B) Chemical change
6. Crystallisation of sugar from its solution is a:
A) Chemical change B) Physical change C) Both D) None
B) Physical change
A) Chemical change B) Physical change C) Both D) None
B) Physical change
7. Photosynthesis in plants is a:
A) Physical change B) Chemical change C) Reversible change D) None
B) Chemical change
A) Physical change B) Chemical change C) Reversible change D) None
B) Chemical change
8. Glowing of an electric bulb is a:
A) Chemical change B) Physical change C) Both D) Nuclear change
B) Physical change
A) Chemical change B) Physical change C) Both D) Nuclear change
B) Physical change
9. Souring of milk is:
A) Physical change B) Chemical change C) Reversible D) Desirable change
B) Chemical change
A) Physical change B) Chemical change C) Reversible D) Desirable change
B) Chemical change
10. Which of the following is reversible?
A) Burning of paper B) Cooking of food C) Melting of wax D) Ripening of mango
C) Melting of wax
A) Burning of paper B) Cooking of food C) Melting of wax D) Ripening of mango
C) Melting of wax
11. Formation of curd from milk is:
A) Physical change B) Chemical change C) Reversible D) No change
B) Chemical change
A) Physical change B) Chemical change C) Reversible D) No change
B) Chemical change
12. Breaking of glass is a:
A) Chemical change B) Physical change C) Both D) None
B) Physical change
A) Chemical change B) Physical change C) Both D) None
B) Physical change
13. Explosion of fireworks is a:
A) Physical change B) Chemical change C) Slow change D) Reversible change
B) Chemical change
A) Physical change B) Chemical change C) Slow change D) Reversible change
B) Chemical change
14. Evaporation of water is a:
A) Chemical change B) Physical change C) Permanent change D) None
B) Physical change
A) Chemical change B) Physical change C) Permanent change D) None
B) Physical change
15. Digestion of food in our body is a:
A) Physical change B) Chemical change C) Mechanical change D) Reversible change
B) Chemical change
A) Physical change B) Chemical change C) Mechanical change D) Reversible change
B) Chemical change
16. Respiration is a:
A) Physical change B) Chemical change C) Both D) None
B) Chemical change
A) Physical change B) Chemical change C) Both D) None
B) Chemical change
17. Dissolving common salt in water is a:
A) Chemical change B) Physical change C) Irreversible D) None
B) Physical change
A) Chemical change B) Physical change C) Irreversible D) None
B) Physical change
18. Blackening of silver articles is a:
A) Physical change B) Chemical change C) Desirable change D) Reversible physical change
B) Chemical change
A) Physical change B) Chemical change C) Desirable change D) Reversible physical change
B) Chemical change
19. Stretching of rubber band is a:
A) Chemical change B) Physical change C) Permanent change D) None
B) Physical change
A) Chemical change B) Physical change C) Permanent change D) None
B) Physical change
20. Which one is an exothermic chemical change?
A) Melting of ice B) Burning of coal C) Evaporation of water D) Dissolving ammonium chloride
B) Burning of coal
A) Melting of ice B) Burning of coal C) Evaporation of water D) Dissolving ammonium chloride
B) Burning of coal
21. The process of photosynthesis is:
A) Exothermic B) Endothermic C) No energy change D) Physical
B) Endothermic
A) Exothermic B) Endothermic C) No energy change D) Physical
B) Endothermic
22. Which of the following involves a chemical change?
A) Boiling of water B) Tearing of paper C) Rusting of iron D) Freezing of water
C) Rusting of iron
A) Boiling of water B) Tearing of paper C) Rusting of iron D) Freezing of water
C) Rusting of iron
23. When a candle burns, the total mass of candle + oxygen:
A) Increases B) Decreases C) Remains same D) Becomes zero
C) Remains same (Law of conservation of mass)
A) Increases B) Decreases C) Remains same D) Becomes zero
C) Remains same (Law of conservation of mass)
24. Sublimation of camphor is a:
A) Chemical change B) Physical change C) Both D) None
B) Physical change
A) Chemical change B) Physical change C) Both D) None
B) Physical change
25. Which is a desirable chemical change?
A) Rusting B) Spoilage of food C) Formation of manure from waste D) Burning of plastic
C) Formation of manure from waste
A) Rusting B) Spoilage of food C) Formation of manure from waste D) Burning of plastic
C) Formation of manure from waste
26. Cooking of food is:
A) Reversible B) Physical change C) Chemical change D) Temporary change
C) Chemical change
A) Reversible B) Physical change C) Chemical change D) Temporary change
C) Chemical change
27. Which change is reversible?
A) Ripening of fruits B) Folding of paper C) Burning of LPG D) Curdling of milk
B) Folding of paper
A) Ripening of fruits B) Folding of paper C) Burning of LPG D) Curdling of milk
B) Folding of paper
28. The best evidence of a chemical change is:
A) Change in colour B) Formation of new substances C) Change in temperature D) Evolution of gas
B) Formation of new substances
A) Change in colour B) Formation of new substances C) Change in temperature D) Evolution of gas
B) Formation of new substances
29. Which of the following is a slow chemical change?
A) Explosion B) Rusting C) Burning D) Digestion
B) Rusting
A) Explosion B) Rusting C) Burning D) Digestion
B) Rusting
30. Making of ice cream involves:
A) Only chemical change B) Only physical change C) Both D) None
C) Both (freezing = physical, reactions in ingredients = chemical)
A) Only chemical change B) Only physical change C) Both D) None
C) Both (freezing = physical, reactions in ingredients = chemical)
31. Which is an irreversible change?
A) Melting of ice B) Burning of wood C) Boiling of water D) Evaporation of petrol
B) Burning of wood
A) Melting of ice B) Burning of wood C) Boiling of water D) Evaporation of petrol
B) Burning of wood
32. Formation of clouds is a:
A) Chemical change B) Physical change C) Both D) Nuclear change
B) Physical change
A) Chemical change B) Physical change C) Both D) Nuclear change
B) Physical change
33. Which of the following produces a new substance?
A) Crushing a tablet B) Baking a cake C) Cutting vegetables D) Dissolving salt
B) Baking a cake
A) Crushing a tablet B) Baking a cake C) Cutting vegetables D) Dissolving salt
B) Baking a cake
34. The green coating on copper vessels is due to formation of:
A) Copper oxide B) Copper carbonate C) Copper sulphate D) Copper nitrate
B) Copper carbonate
A) Copper oxide B) Copper carbonate C) Copper sulphate D) Copper nitrate
B) Copper carbonate
35. Which is a physical change?
A) Corrosion of aluminium B) Sublimation of iodine C) Digestion of bread D) Burning of LPG
B) Sublimation of iodine
A) Corrosion of aluminium B) Sublimation of iodine C) Digestion of bread D) Burning of LPG
B) Sublimation of iodine
36. In chemical changes, mass is:
A) Lost B) Gained C) Conserved D) Destroyed
C) Conserved
A) Lost B) Gained C) Conserved D) Destroyed
C) Conserved
37. Ripening of mango is a:
A) Fast chemical change B) Slow chemical change C) Physical change D) Reversible change
B) Slow chemical change
A) Fast chemical change B) Slow chemical change C) Physical change D) Reversible change
B) Slow chemical change
38. Which of the following is a chemical change?
A) Magnetisation of iron B) Formation of dew C) Burning of incense stick D) Freezing of juice
C) Burning of incense stick
A) Magnetisation of iron B) Formation of dew C) Burning of incense stick D) Freezing of juice
C) Burning of incense stick
39. During a chemical change, energy is:
A) Always absorbed B) Always released C) Either absorbed or released D) Never involved
C) Either absorbed or released
A) Always absorbed B) Always released C) Either absorbed or released D) Never involved
C) Either absorbed or released
40. Which is NOT a chemical change?
A) Fermentation B) Condensation C) Combustion D) Rancidity
B) Condensation
A) Fermentation B) Condensation C) Combustion D) Rancidity
B) Condensation
41. The process of rusting can be prevented by:
A) Painting B) Galvanisation C) Both A and B D) None
C) Both A and B
A) Painting B) Galvanisation C) Both A and B D) None
C) Both A and B
42. Which gas is evolved when baking soda reacts with vinegar?
A) Oxygen B) Hydrogen C) Carbon dioxide D) Nitrogen
C) Carbon dioxide
A) Oxygen B) Hydrogen C) Carbon dioxide D) Nitrogen
C) Carbon dioxide
43. Which change is endothermic?
A) Burning of candle B) Photosynthesis C) Respiration D) Combustion of fuel
B) Photosynthesis
A) Burning of candle B) Photosynthesis C) Respiration D) Combustion of fuel
B) Photosynthesis
44. Which of the following is a physical property?
A) Flammability B) Reactivity with acid C) Boiling point D) Toxicity
C) Boiling point
A) Flammability B) Reactivity with acid C) Boiling point D) Toxicity
C) Boiling point
45. The smell of rotten eggs is due to:
A) Hydrogen sulphide B) Carbon dioxide C) Oxygen D) Nitrogen
A) Hydrogen sulphide (chemical change)
A) Hydrogen sulphide B) Carbon dioxide C) Oxygen D) Nitrogen
A) Hydrogen sulphide (chemical change)
46. Which is a reversible physical change?
A) Inflating a balloon B) Baking bread C) Frying an egg D) Burning matchstick
A) Inflating a balloon
A) Inflating a balloon B) Baking bread C) Frying an egg D) Burning matchstick
A) Inflating a balloon
47. Rancidity in chips is prevented by filling packets with:
A) Oxygen B) Nitrogen C) Carbon dioxide D) Hydrogen
B) Nitrogen
A) Oxygen B) Nitrogen C) Carbon dioxide D) Hydrogen
B) Nitrogen
48. Which of the following is a chemical change?
A) Melting of butter B) Churning of milk to butter C) Fermentation of milk D) Freezing of milk
C) Fermentation of milk
A) Melting of butter B) Churning of milk to butter C) Fermentation of milk D) Freezing of milk
C) Fermentation of milk
49. The process of electrolysis of water is a:
A) Physical change B) Chemical change C) Reversible physical change D) None
B) Chemical change
A) Physical change B) Chemical change C) Reversible physical change D) None
B) Chemical change
50. The most reliable test for a chemical change is:
A) Change in temperature B) Change in colour C) Formation of a new substance D) Evolution of gas
C) Formation of a new substance
A) Change in temperature B) Change in colour C) Formation of a new substance D) Evolution of gas
C) Formation of a new substance
This is the definition of a chemical change.