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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