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What is a Combined Change?
It is a process where both physical changes and chemical changes happen at the same time .
- Burning candle shows both physical and chemical changes together.
- Melting wax is a physical change - no new substance.
- Burning vapour is a chemical change - new substances form.
- Evaporation of melted wax is also physical change .
Activity 5.7: Think, pair, and share
What you need:
- A burning candle
- Observation skills
- Partner for discussion
What to do:
- Step 1: Observe the burning candle carefully
- Step 2: Identify what changes are happening
- Step 3: Discuss with your partner about these changes
- Step 4: Share your observations with the class
Observations
What you see:
- Solid wax near the wick becomes liquid
- Liquid wax gets carried up the wick
- Wax vapour forms near the hot flame
- Bright flame burns with heat and light
- New substances like carbon dioxide and water vapour form
Why this happens:
We have studied that physical changes change appearance but same substance remains, while chemical changes form new substances . This is why burning candle shows both types together.
- Melting and evaporation are physical changes
- Burning vapour is a chemical change
- Both processes happen simultaneously in same candle
Section Summary: Can Physical and Chemical Changes Occur in the Same Process?
🔎 Know a Scientist
The candle you just observed has long been an object of curiosity for several scientists, including Michael Faraday , who made significant contributions to several areas of science.
In the nineteenth century, Faraday delivered a series of lectures called Chemical History of a Candle . Faraday believed that the candle was the perfect object to introduce scientific study . Through it, he discussed differences between various physical and chemical processes like melting , vaporisation , and combustion .
