Chapter 6: Physical and Chemical Changes

Q11Written answer

State whether the following statements are true or false:

(a) When a candle burns, both physical and chemical changes take place.

(b) Anaerobic bacteria digest animal waste and produce biogas.

(c) Ships suffer a lot of damage though they are painted.

(d) Stretching of rubber band is not a physical change.

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Ans:

(a) The given statement is true.

(b) The given statement is true.

(c) The given statement is true.

(d) The given statement is false. Stretching of a rubber band is a ‘physical change’.

Q12Written answer

Melting of wax is a change where a solid changes to liquid state. Give one more such change which you observe in your surroundings.

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Ans: When a candle is lit, two things happen at the same time. The first step is to melt the wax, and the second step is to burn the wax. In these cases, melting wax is a physical change, whereas burning wax is a chemical reaction. Because burning causes oxidation of wax, which is a chemical change. Another example, according to the provided criteria, is 'Melting of ice.'

Q13Written answer

What kind of change is shown by tearing of paper?

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Ans: Paper tearing is a physical change that cannot be undone.

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