Physical and Chemical Changes — Question 8
Back to all questionsQuestion 8
What do you observe when:
(a) Water is boiled
(b) a piece of paper is burnt
(c) some ice cubes are kept in a glass tumbler
(d) solid ammonium chloride is heated
(e) an iron nail is kept in tap water for few days
(f) a spoon of sugar is heated in a pan
(g) a lighted match stick is brought near the mouth of the test tube containing hydrogen gas
(h) quick lime is dissolved in water
(i) little amount of curd is added to a bowl containing warm milk and kept for five hours?
(a) When water is boiled it converts into vapours.
(b) When a piece of paper is burnt, it changes into ash.
(c) When some ice cubes are kept in a glass tumbler, water droplets are seen on the outer wall of the tumbler and after sometime ice cubes changes into water.
(d) When solid ammonium chloride is heated, it directly changes into vapours.
(e) When an iron nail is kept in tap water for few days a reddish brown coating is seen on the nail.
(f) When a spoon of sugar is heated in a pan it first melts and changes its colour to reddish-brown and finally it turns black and gets charred.
(g) When a lighted match stick is brought near the mouth of the test tube containing hydrogen gas a pop sound is heard and the flame of the match stick gets extinguished.
(h) When quick lime is dissolved in water a large amount of heat energy is evolved along with a hissing sound is produced.
(i) The bowl containing milk changes into curd.
ICSE Class VII Chemistry Chapter 2 12 Marks
Physical and Chemical Changes — Quick Study Guide
Changes around us are classified as physical (no new substance formed) or chemical (new substance formed). Understanding the difference is fundamental to chemistry.
Key Definitions
- Physical change: No new substance formed, usually reversible (e.g., melting ice, dissolving sugar)
- Chemical change: New substance formed, usually irreversible (e.g., burning, rusting, cooking)
- Exothermic: Reaction that releases heat (e.g., burning fuel)
- Endothermic: Reaction that absorbs heat (e.g., photosynthesis)
Six Signs of Chemical Change
Colour change, gas evolution, temperature change, precipitate formation, smell change, light/sound emission.
Exam Tips
- Burning a candle = BOTH physical and chemical change
- Dissolving salt/sugar in water = physical change (recoverable)
- Not all physical changes are reversible (tearing paper)
- Learn the comparison table (6 differences) thoroughly
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