Changes Around Us

Samacheer Book Back Questions And Answers For Science Standard 7 Term 2 “Changes Around Us“

I. Choose the best answer:
1. When a woollen yarn is knitted to get a sweater, the change can be classified as _____.
(a) Physical change
(b) Chemical change
(c) Endothermic change
(d) Exothermic change

2. _____of the following are endothermic changes.
(a) Condensation and melting
(b) Condensation and freezing
(c) Evaporation and melting
(d) Evaporation and freezing

3. The chemical change is _____.
(a) Water to clouds
(b) Growth of tree
(c) Cow dung to bio-gas
(d) Ice-cream to molten ice-cream

4. _____ is an example of a periodic change
(a) Earthquake
(b) Formation of rainbow in sky
(c) Occurrence of tides in seas
(d) Showering of rain

5. _____ is not a chemical change.
(a) Dissolution of ammonia in water
(b) Dissolution of carbon-dioxide in water
(c) Dissolution of oxygen in water
(d) Melting of polar ice caps

II. Fill in the blanks:
1. Filling up a balloon with hot air is a _____ change.
2. Stretching gold coin into a ring is a _____ change.
3. Opening a gas cylinder knob converts _____ fuel into _____ fuel. This is an example of _____ change.
4. Spoiling of food is a _____ change.
5. Respiration is a _____change.

Answers:
1. Physical
2. Physical
3. Liquid, gaseous, chemical
4. Chemical
5. Periodic change

III. True or False – If False give the correct answer:
1. Cutting of cloth is an example of a periodic change.
2. Taking a glass of water and freezing it by placing it in the freezer is a chemical change.
3. A bean plant collecting sunlight and turning it into bean seeds is an example of physical and non-periodic change.
4. If the chemical properties of a substance remain unchanged and the appearance or shape of a substance changes it is called a periodic change.
5. Tarnishing of silver is an example of endothermic change.

Answers:
1. False (Cutting of cloth is an example of a physical change)
2. False (Taking a glass of water and freezing it by placing it in the freezer is a physical change)
3. False (A bean plant collecting sunlight and turning it into bean seeds is an example of chemical and non-periodic change)
4. False (If the chemical properties of a substance remain unchanged and the appearance or shape of a substance changes it is called a fossil change)
5. False (Tarnishing of silver is an example of chemical change)

IV. Match the following:
1. Melting                           A. Change of state from liquid to solid         a. Ticking of clock
2. Condensation                 B. Change of state from liquid to gas           b. Formation of ice cube
3. Evaporation                    C. Change of state from solid to liquid         c. Collecting flowers
4. Freezing                         D. Change of state from gas to liquid           d. Ice cube to water
5. Periodic change             E. Occurs at irregular time intervals               e. Water to steam
6. Non-periodic change     F. Occurs at regular time intervals                 f. Steam to water drops

Answers:
1. C. d
2. D. f
3. B. e
4. A. b
5. E. a
6. F. c

V. Classify the following changes as physical and chemical changes:

1. A rough piece of wood is sanded and polished resulting in change in texture, Rusting of a iron nail, Painting the grill, Bending a paper clip, Pounding silver into thin plate, Rolling the chapathi dough into thin wire, Occurrence of day and night, eruption of volcano, burning of matchstick, dosa from the batter, blinking of eyelids, occurrence of a thunderstorm, rotation of the earth, formation of eclipses.

Answers:
Physical changes
Bending a paper clip.
Pounding silver into thin plate.
Rolling a chapathi dough into thin wire.
Occurrence of a day and night.
Blinking of eyelids.
Occurrence of a thunderstorm.
Rotation of the earth.
Formation of eclipses.
Painting the grill.
A rough piece of wood is sanded and polished resulting in change in texture.
Dosa from the batter.

Chemical changes
1. Rusting of a iron
2. Eruption of volcano
3. Burning of matchstick.

VI Analogy:
1. Physical Change: Boiling::Chemical Change: _____.
2. Wood to saw dust: _____:: Wood to Ash: Chemical change
3. Forest fire: _____ change::Change in period in a school: periodic change

Answers:
1. Burning
2. Physical change
3. Non-periodic

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