Question

Class 7 science Examples of both physical and chemical changes

Answer 1

Physical change
If we put a glass of water in the refrigerator and take it out after some time it changes into ice .But after some time it is kept out it again changes into water.Thus we get back the original substance without any change in it's chemical properties.So this is a physical change.
Chemical change
Of we burn a piece of paper we get two new substances-ash and smoke .We cannot get back paper again from ash and smoke. So I his is a chemical change.

Answer 2

ANSWER
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First of all we should know the difference between physical change and chemical change..

⇒ Physical Change --

→ No new substance is formed.

→ The change is temporary and can be easily removed.

→ The weight of the substances undergoing a physical change does not change.

→ Generally, energy in the form of heat, light, etc.., is neither evolved nor absorbed during the change.

⇒ Chemical Change --

→ New substance is formed.

→ The change is permanent and cannot be reversed by simple physical methods.

→ The weight of the individual substances undergoing a chemical change either increases or decreases. However, the total weight remains the same.

→ Energy in the form of heat, light, electricity, etc.., is generally evolved or absorbed during the change.

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⇒ Examples of physical changes

→ Heating of wax.

→ Boiling of water.

→ Melting of ice.

→ Dissolving of salt in water.


⇒ Examples of chemical changes

→ Making butter from cream.

→ Ripening of a fruit.

→ Growing of human hair and nails.

→ Decomposition of red lead.

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