question_answer 59)

  Classify each of the following, as a physical or a chemical change. Give reasons. (a) Drying of a shirt in the sun.                                   (b) Rising of hot air over a radiator. (c) Burning of kerosene in a lantern.       (d) Change in the colour of black tea on adding lemon juice to it. (e) Churning of milk cream to get butter.

Answer:

  (a) Physical change because evaporation of water takes place but no change occurs in the composition of the substance. (b) Physical change because it is also involving only movement of air, no change in composition of air. (c) First physical change, when kerosene vaporises. After that, burning of kerosene is a chemical change as new products are formed. (d) Physical change as there occurs only the dissolution. (e) Physical .change as there is no change in composition. Only the separation of components takes place by the physical phenomenon, centrifugation.