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Important Questions Chapter 5 Class 7 Science Curiosity NCERT

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Changes Around Us: Physical and Chemical


Short Questions

1. What is a physical change?

Answer: A change where no new substance is formed, like melting ice.

2.What is a chemical change?

Answer: A change where new substances are formed, like burning wood.

3.Is melting ice a physical or chemical change?

Answer: Physical change.

4.What happens when lime water turns milky?

Answer: It shows the presence of carbon dioxide.

5.What is rusting?

Answer: A chemical change where iron forms rust (iron oxide).

6.What is combustion?

Answer: A chemical reaction with oxygen that produces heat or light.

7.  Can you reverse the chopping of vegetables?

Answer: No.

8.What is the ignition temperature?

Answer: The minimum temperature at which a substance catches fire.

9. Is folding paper a physical or chemical change?

Answer: Physical change.

10.What is weathering?

Answer: The process of breaking rocks into smaller pieces by physical or chemical changes.


Long Questions

1. What is the difference between physical and chemical changes?

Answer: Physical changes only affect the appearance, like shape or size, without forming new substances. Chemical changes create new substances, like rust or carbon dioxide.

2.Why does a candle burning involve both physical and chemical changes?

Answer: The wax melting and evaporating are physical changes. The burning of wax vapor to produce new substances like carbon dioxide is a chemical change.

3.How can you test for carbon dioxide using lime water?

Answer: Blow air or pass gas through lime water; if it turns milky, carbon dioxide is present. This happens because carbon dioxide reacts with lime water to form calcium carbonate.

4.Why is rusting considered a chemical change?

Answer: Rusting forms a new substance, iron oxide, when iron reacts with oxygen and water. This cannot be reversed, making it a chemical change.

5.What is erosion, and why is it a physical change?

Answer: Erosion is the movement of rock, soil, or sand by wind or water. It is a physical change because no new substances are formed, only the location or shape changes.

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