The Candle''s Secret
A burning candle shows both kinds of change at once.
What this lesson covers
Why it matters
Watch a lit candle closely. The wax near the flame melts into a clear pool, while up in the flame the wax is being burned away into gases you cannot see. One candle, two very different changes.
Predict first
The solid wax of a candle melts into a liquid pool near the flame. When this pool cools, it hardens back into wax. What kind of change is the melting?
Melting and re-hardening of wax is a physical change: it is reversible and no new substance is made. But burning the wax is a chemical change, because new gases form. A candle shows both at once.
- A chemical change, because new substances form
- A physical change, because it is still wax and can be reversed — correct
- No change at all
- A change that gives out new gases
What you do
A burning candle does many things at once. Sort each one as a PHYSICAL change or a CHEMICAL change.
Check yourself
Why is the melting of candle wax called a physical change?
Melting only changes the state of the wax. It is still wax and can be turned back to solid on cooling, so it is a physical change.
Why is the burning of candle wax a chemical change?
When wax burns it combines with oxygen to make new substances, carbon dioxide and water vapour, and cannot be reversed. That makes it a chemical change.
What is special about a burning candle compared with most everyday examples?
A candle is a classic example because the wax melts and vaporises (physical) while it also burns (chemical), so both changes occur at the same time.
- It is still wax and the change can be reversed — correct
- A brand new substance is formed
- It cannot be reversed
- It gives out new gases
- New substances such as carbon dioxide and water are formed — correct
- The wax simply melts and can be re-set
- Nothing new is produced
- It can easily be reversed
- It shows a physical change and a chemical change happening together — correct
- It shows only a physical change and nothing else
- It shows no change of any kind
- It shows only a chemical change and nothing else