Chapter 2: Is Matter Around Us Pure?

Physical & Chemical Changes

Physical Change

A change in physical properties without change in chemical composition.

Examples:

  • ❄️ Ice → Water → Steam
  • 🧂 Dissolving salt in water
  • ✂️ Cutting paper
  • 🧈 Melting butter

Key Point: The substance remains chemically the same


Chemical Change

A change where new substances with different properties are formed.

Examples:

  • 🔥 Burning wood/paper
  • 🦀 Rusting of iron
  • 🍞 Cooking/digestion of food
  • ⚡ Electrolysis of water

Key Point: Chemical composition changes, new substances formed


Comparison

PropertyPhysical ChangeChemical Change
CompositionSameDifferent
New substanceNot formedFormed
ReversibilityUsually reversibleUsually irreversible
EnergySmall changeLarge change

🕯️ Burning Candle — Both Changes!

TypeChange
PhysicalWax melts (solid → liquid)
ChemicalWax burns, produces CO₂ and H₂O

📝 Classify These Changes

ProcessType
Cutting treesPhysical
Melting butterPhysical
Rusting of ironChemical
Boiling waterPhysical
Electrolysis of waterChemical
Dissolving saltPhysical
Burning paperChemical
Visualizer
🧊 Solid
Absorbs heat
💧 Liquid
Melting (Fusion)
at 0°C / 273K

Interactive Visualization