(a) What can we conclude from burning of a candle with respect to physical and chemical changes?
(b) Is cooking of rice a reversible change?
[3 MARKS]
(a) What can we conclude from burning of a candle with respect to physical and chemical changes?
(b) Is cooking of rice a reversible change?
[3 MARKS]
Each part: 1.5 Marks
(a) When candle burns, both physical and chemical changes take place. On burning, the candle wax melts but can be solidified again on cooling. This shows that melting of wax is a physical change.
The burning of candle also produces light and carbon dioxide. Hence, it is also a chemical change.
(b) A reversible change is a type of change in which a substance that is undergoing a change can be recovered in its original form. An irreversible change is a type of change in which a substance cannot be reobtained in its original form. In the cooking of rice, raw rice cannot be obtained from cooked rice. Therefore, this change is an irreversible change.
Each part: 1.5 Marks
(a) When candle burns, both physical and chemical changes take place. On burning, the candle wax melts but can be solidified again on cooling. This shows that melting of wax is a physical change.
The burning of candle also produces light and carbon dioxide. Hence, it is also a chemical change.
(b) A reversible change is a type of change in which a substance that is undergoing a change can be recovered in its original form. An irreversible change is a type of change in which a substance cannot be reobtained in its original form. In the cooking of rice, raw rice cannot be obtained from cooked rice. Therefore, this change is an irreversible change.
