NCERT Solutions Curiosity Chapter 5 .4 Can Physical and Chemical Changes Occur in the Same Process? — Activity 5.7: Think, pair, and share
Book page 655 Updated on2026-09-05
Q1.
Look at the Fig. 5.9. Analyse what students are discussing about the burning candle. What do you think?
Answer
All the students are partly right — and taken together they describe the whole story. The burning of a candle involves both physical and chemical changes at the same time.
What the student says
Is it correct?
Type of change
“The wax melts and evaporates…”
Correct — solid wax melts and the liquid wax turns into vapour near the flame
Physical
“Wax melts, flows, and solidifies in different shapes…”
Correct — the wax that runs down the side cools and sets again
Physical
“Maybe the wick draws up the liquid wax…”
Correct — the wick soaks up molten wax and carries it to the flame
Physical
“I think the wax burns, and new substances are formed…”
Correct — the wax vapour burns in the oxygen of the air
Chemical
What actually happens: the wax of the candle melts, is carried up the wick, and evaporates due to the heat of the flame. It is this vapour of wax that burns to produce the flame.
The melting, flowing, solidification and evaporation of wax are physical changes; the burning of the wax vapour is a chemical change.
Did you know? Michael Faraday found the candle so rich a subject that he gave a whole series of lectures on it, Chemical History of a Candle, in the nineteenth century. He used it to show the difference between melting, vapourisation and combustion.