Q. 13.8( 112 Votes )
Classify the following as chemical or physical changes:
(i) cutting of trees
(ii) melting of butter in a pan
(iii) rusting of almirahs
(iv) boiling of water to form steam
(v) passing of electric current through water and the water breaking down into hydrogen and oxygen gases
(vi) dissolving common salt in water
(vii) making a fruit salad with raw fruits, and
(viii) burning of paper and wood
Answer :
Chemical changes are rusting of almirahs, passing of electric current through water and water breaking down into hydrogen and oxygen gases, burning of paper and wood. The chemical properties of all of these substances have changed and new substances have been formed as a result of these changes. Rust is an oxide of iron which is a new substance formed on the surface of almirah. Hydrogen and oxygen are also new compounds which are produced after passing electric current through water. Burning of paper is a chemical reaction which has changed in the chemical properties of paper.
Physical changes are melting of butter in a pan, cutting of trees, boiling of water to form steam, dissolving common salt in water and making a fruit salad with raw fruits. Physical changes occur without any change in chemical composition of a substance. Melting butter and boiling of water to form steam has only changed the physical states of these substances without causing any change in their chemical composition.
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