State the differences between physical and chemical changes, giving one example of each.

**The reasoning** This is an essay question, not multiple choice, so let me break down what examiners want: **Physical Change** happens when a substance changes form but keeps its chemical identity. The particles stay the same; only their arrangement changes. It's usually **reversible**. *Example:* Ice melting into water. The H₂O molecules remain H₂O whether solid or liquid. You can freeze it back. **Chemical Change** creates entirely new substances with different properties. The original particles break apart and rearrange into new combinations. Usually **irreversible**. *Example:* Burning wood into ash and smoke. The cellulose in wood reacts with oxygen, forming CO₂, water vapor, and carbon residue. You can't "unburn" it back to wood. **Why students lose marks** Many give vague differences like "physical is temporary, chemical is permanent" without explaining the particle-level change. Others pick poor examples (like dissolving sugar — tricky because it looks physical but involves molecular dispersion). **Quick takeaway** Physical change = same substance, different look; Chemical change = brand new substance formed. Always mention reversibility and give a clear, everyday example for full marks.