Physical & Chemical Changes
Year 7 ⚗️ Chemical Reactions Tell apart reversible physical changes from irreversible chemical changes.
🔄 Physical Changes
In a physical change, no new substance is formed. The change is usually reversible and the chemical composition stays the same.
Examples: Melting ice, dissolving salt in water, boiling water, bending a wire. All are reversible.
Physical changes are reversible — you can recover the original substance.
⚗️ Chemical Changes
In a chemical change, new substances with different properties are formed. Chemical changes are usually irreversible and involve energy changes.
Signs of a chemical change:
• New substance formed (different colour, smell, properties)
• Gas produced (bubbles) | Temperature change | Precipitate forms
• New substance formed (different colour, smell, properties)
• Gas produced (bubbles) | Temperature change | Precipitate forms
Examples: Burning wood, rusting iron, cooking an egg, acid + metal reaction.
⚖️ Conservation of Mass
Mass is conserved in all chemical reactions — no atoms are created or destroyed.
Conservation of Mass
$$\text{Total mass of reactants} = \text{Total mass of products}$$Example: 2 g H₂ + 16 g O₂ → 18 g H₂O. Mass is conserved. ✓
Ready to test yourself? Click the Quiz tab above to practise questions on this topic!
Interactive Demonstration — Physical & Chemical Changes
Classify each change as Physical or Chemical.
Click each change to classify it.
🔄 Physical vs Chemical Change Sorter
Calculate energy changes during physical changes (q = mcΔT).