Samacheer Kalvi 7th Science Term 2 Unit 3 Book Back Questions and Answers:

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TN State Board Class 7th Science Subject Term 2 Unit 3 one mark and two mark solutions guide PDF available below.

Science – Term 2

Unit 3 – Changes Around Us

I. Choose the best answer :

1. When a woolen 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
Answer: (a) physical change

2. _________ of the following are endothermic changes.
(a) Condensation and melting
(b) Condensation and freezing
(c) Evaporation and melting
(d) Evaporation and freezing
Answer: (a) Condensation and melting

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
Answer: (c) cow dung to bio-gas

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

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

II.Fill in the blanks :

1. Filling up a balloon with hot air is a _______ change.
2. Stretching a 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.

Answer:

1. physical
2. physical
3. liquid, gaseous, chemical
4. chemical
5. exothermic chemical

III. True or False – If False gives the correct answer :

1. Cutting of cloth is an example of a periodic change.
Answer:
False, Cutting of cloth is an example of a physical change.

2. Taking a glass of water and freezing it by placing it in the freezer is a chemical change.
Answer:
False, Taking a glass of water and freezing it by placing it in the freezer is a physical change

3. A bean plant collecting sunlight and turning it into bean seeds is an example of physical and non-periodic change.
Answer:
False, A bean plant collecting sunlight and turning it into bean seeds is an example of chemical 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.
Answer:
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. Tarnishing of silver is an example of endothermic change.
Answer:
False, Tarnishing of silver is an example of change.

IV. Match the following:

A	B	C
1. Melting	Change of state from liquid to solid	Ticking of clock
2. Condensation	Change of state from liquid to gas	Formation of ice cube
3. Evaporation	Change of state from solid to liquid	Collecting flowers
4. Freezing	Change of state from gas to liquid	Ice cube to water
5. Periodic change	Occurs at irregular time intervals	Water to steam
6. Non-periodic change	Occurs at regular time intervals	Steam to water drops

Answer:

A	B	C
1. Melting	Change of state from liquid to solid	Ice cube to water
2. Condensation	Change of state from liquid to gas	Steam to water drops
3. Evaporation	Change of state from solid to liquid	Water to steam
4. Freezing	Change of state from gas to liquid	Formation of ice cube
5. Periodic change	Occurs at irregular time intervals	Ticking of clock
6. Non-periodic change	Occurs at regular time intervals	Collecting flowers

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

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

Physical changes:

1. Bending a paper clip.
2. Pounding silver into a thin plate.
3. Rolling a chapati dough into thin wire.
4. Occurrence of a day and night.
5. Blinking of eyelids.
6. Occurrence of a thunderstorm.
7. Rotation of the earth.
8. Formation of eclipses.
9. Painting the grill.
10. A rough piece of wood is sanded and polished resulting in a change in texture.
11. Dosa from the batter.

Chemical changes:

1. Rusting of an iron
2. Eruption of volcano
3. Burning of matchstick.

VI Analogy:

1. Physical Change: Boiling::Chemical Change: ________
Answer: Burning.

2. Wood to sawdust: _________ :: Wood to Ash: Chemical change
Answer: Physical change.

3. Forest fire: ________ change::Change in the period in a school: periodic change
Answer: Non-periodic.

VII. Very short answer type question :

1. State two examples of periodic changes.
Answer: Seasonal changes, the motion of the hands of a clock.

2. Mention any two exothermic reactions.
Answer: Burning of magnesium ribbon and burning of a candle.

3. Cold milk is heated and it becomes hot. Which type of change it is?
Answer: Reversible.

4. What type of change is the artificial ripening of fruit?
Answer: Irreversible chemical change.

5. What type of change is the coloring of a paper?
Answer: Physical change.

6. Growing nails is a periodic change. Why?
Answer: Growing nail is a periodic change because it occurs periodically at regular intervals.

7. What type of energy changes is associated when the ice melts?
Answer:

1. Physical change
2. Endothermic (heat energy is absorbed)

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