NCERT Class VI Science Solutions: Chapter 6-Changes Around us Part 2

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Watch Video Lecture on YouTube: NCERT Class 6 Science Chapter 6: Changes Around Us

NCERT Class 6 Science Chapter 6: Changes Around Us

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Question 5:

Give examples to explain the difference between changes that can or cannot be reversed.

Answer:

Examples of Reversible Changes:

  • Melting of Ice into water. By freezing the water we can obtain ice again.

  • Folding a paper: By unfolding it, we can undo the change.

  • Hot milk to cold milk: By boiling milk, we can make it warm.

Example of Irreversible Changes:

  • Burning of candle.

  • Bursting of crackers.

  • Cutting of trees.

Question 6:

A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilised. Can the change in POP be reversed?

Answer:

When water is added to POP, it undergoes a chemical change. Its composition changes and is converted into another substance. Since it is a chemical change, so it cannot be reversed.

This image shows examples of Plaster of Peris (POP)

Examples of Plaster of Peris

Question 7:

A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?

Answer:

Due to water, cement hardens and its composition changes. Since it is a chemical change which cannot be reversed.

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