Physical vs Chemical Changes
The difference between rearranging furniture and burning down the house.
🏡 The House Scenario
Imagine you own a house. One day, you move all the furniture around — the sofa is now in the kitchen, the table is in the bedroom. Has your house changed? Superficially yes. But it is the same house, same furniture, same atoms. That is a Physical Change.
Now imagine the house catches fire. After the inferno, you have ash, smoke, CO₂, and water vapour. The wood molecules have been chemically destroyed and new substances have been formed. That is a Chemical Change.
⚗️ Physical Change
- ✓No new substance is formed
- ✓Often easily reversible
- ✓Same atoms, rearranged
- ✓No new bonds formed or broken permanently
Examples:
Melting, boiling, dissolving, crushing, bending
🔥 Chemical Change
- ✗A new substance IS formed
- ✗Usually difficult to reverse
- ✗Different atoms/molecules
- ✗New bonds are formed or broken
Clues in the lab:
Colour change, gas produced, temperature change, precipitate formed
Examiner's Trap #1
Students write "reversible" as the definition of physical change. Wrong! The Cambridge mark scheme wants: "no new substance is formed." Reversibility is a consequence, not the definition.
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