Q46 of 252 Page 81

What is a chemical change?

Give two examples of chemical changes.

Those changes in which new substances are formed, are called chemical changes. A chemical change is also called a chemical reaction. In a chemical change, the substances involved, change their identity . They get converted into entirely new substances. The new substances usually cannot be returned to their original form. This means that chemical changes are usually irreversible.

Burning of candle and burning of hydrogen in oxygen to form water.


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45

Which of the following do not exhibit Tyndall effect?

Starch solution, Sugar solution, Ink, Salt solution, Copper sulphate solution, Ammonium chloride solution, Fog, Smoke, Car exhausts.

 46

(a) What is a physical change? Give two examples of physical changes.

 47

Give the main differences between physical changes and chemical changes.

 47

Which of the following are chemical changes and which physical? Give reason.

(i) a glass bottle breaking


(ii) coal burning in air


(iii) making a cake


(iv) wool being knitted into a sweater