Changes Around Us Physical and Chemical Class 7 Short Question Answer

Changes Around Us Physical and Chemical Class 7 Short Question Answer

Changes Around Us Physical and Chemical Class 7 Short Question Answer

Question 1.

Explain why rusting is considered a chemical change.

Answer:

Rusting is considered a chemical change because it involves the formation of a new substance, iron oxide, when iron reacts with oxygen and moisture.

Question 2.

Describe in brief the process of combustion.

Answer:

Combustion is a chemical reaction that occurs when a substance reacts with oxygen, resulting in the release of heat and light, along with the formation of new products.

Question 3.

How can you demonstrate that in exhaling, carbon dioxide is produced?

Answer:

By blowing air into lime water, it turns milky due to the formation of calcium carbonate, indicating that carbon dioxide from exhaled air is reacting with the lime water.

Question 4.

Explain the process of rusting and its significance.

Answer:

Rusting occurs when iron reacts with oxygen and moisture, forming iron oxide. It is significant as it weakens structures made of iron, leading to corrosion and potential structural failure.

Question 5.

Describe how to demonstrate that oxygen is necessary for combustion using a candle.

Answer:

Light two candles; cover one with a glass tumbler. The covered candle extinguishes due to oxygen depletion, demonstrating that oxygen is essential for combustion to continue.

Question 6.

What are the observable signs of a chemical change?

Answer:

Observable signs of a chemical change include colour change, gas production, formation of a precipitate, and energy changes in the form of heat or light.