Question

When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.

Answer 1

Physical change:

• "The changes in which the physical properties of the substances are changed are called a physical change."
• Chemical composition remains the same in a physical change.

Chemical change:

• "The changes in which the chemical properties of the substances are changed are called a chemical change."
• Chemical composition changes in a chemical change.

Burning of a candle:

• Physical change - The melting wax when a candle burn is a physical change that occurs in the process. The wax again solidifies on cooling. It is a reversible process.
• Chemical change - The wax near the wick of the candle vapourises and undergoes a chemical change. It produces Carbon soot, Carbon dioxide, water vapours, heat and light.

Another example:

• Another example in which both physical and chemical change occurs is the digestion of food.
• In this process, the larger food particles are broken into smaller ones which is a physical change.
• The chemical action of enzymes and Hydrochloric acid on the food is a chemical change.