One candle, two kinds of change

The idea

One process can involve both kinds of change: in a burning candle, the melting, solidification and evaporation of wax are physical changes, while the burning of wax vapour is a chemical change.

A burning candle

A candle burns. Its wax melts, rises up the wick, turns to vapour, and the vapour burns with a flame.

What kind of change is a burning candle?

• Only physical changes
• Only chemical changes
• Both kinds of change

Four places on a candle

Tap a numbered place on the candle. Read what happens there. Then choose: physical change or chemical change.

Both kinds, one process

The melting, solidification and evaporation of wax are physical changes. The burning of the vapour is a chemical change. So the burning of a candle involves both physical and chemical changes.

• Place | What happens | Kind of change
• 1 Top of the candle | melting | physical
• 2 Near the wick | evaporation | physical
• 3 In the flame | the vapour burns | chemical
• 4 Down the side | solidification | physical

Notes

A burning candle has both kinds of change. Melting, solidification and evaporation of wax are physical changes. The burning of the vapour is a chemical change.

Check yourself

Which of these is the chemical change in a burning candle?

The wax of a candle melts, evaporates and its vapour burns. Which changes are involved?

Liquid wax runs down the side of a candle and becomes hard again. What kind of change is this?

Melting, evaporation, solidification and burning of the vapour all happen in a candle. How many of these four are physical changes?

Answer: 3

Three: melting, evaporation and solidification. The burning of the vapour is the chemical change.

• Solid wax melting at the top. Melting is a physical change. It is still wax.
• The wax vapour burning — correct. Yes! The vapour burns, and new substances form.
• Liquid wax turning hard again. Turning hard is solidification, a physical change.
• Both kinds of change — correct. Yes! Melting and evaporation are physical. Burning of the vapour is chemical.
• Only physical changes. The burning of the vapour is a chemical change.
• Only chemical changes. Melting and evaporation are physical changes.
• It is a chemical change. The wax is still wax. No new substance forms.
• Nothing changes at all. The wax changes from liquid to solid. It is a physical change.
• It is a physical change — correct. Yes! It is solidification. The wax is still wax.