OpenOlympiad
Concept 4 of 8Foundation
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Chemical changes

A chemical change creates NEW substances with different properties.

Telltale signs of chemical change:

  • Colour change (iron → brown rust)
  • Gas evolved (baking soda + vinegar → bubbles)
  • New smell (egg cooking)
  • Heat or light given off (burning)
  • Sound (explosion)
  • Permanent, cannot be reversed
Example
Baking soda + vinegar → vigorous fizz (CO₂ gas). That fizz tells you new substances have formed.
💡 Tip:Most chemical changes are irreversible by simple physical means.
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5 questions to check what you just read.

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  1. Q1.Sign of a chemical change:
  2. Q2.Example of chemical change:
  3. Q3.Vinegar + baking soda bubbles because:
  4. Q4.Cooking an egg is:
  5. Q5.Which suggests a chemical change?