Educational worksheet on physical and chemical changes, featuring examples and matching exercises.

Absolutely! Let's solve this worksheet step by step.

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## Part 1: Identify whether they are physical or chemical changes

Key Concepts:

- Physical Change: A change in the form or state of matter without changing its chemical composition. No new substances are formed. Often reversible.
- Chemical Change: A change where one or more substances are transformed into new substances with different chemical properties. Usually irreversible and involves breaking/forming chemical bonds.

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Let’s analyze each item:

1. Liquid water freezes and becomes a solid.
→ Water (H₂O) is still H₂O, just in solid form (ice). No new substance.
✔ Physical

2. A metal object rusts and an orange substance appears.
→ Rust is iron oxide — a new substance formed from iron reacting with oxygen and water.
✔ Chemical

3. Bacteria transforms milk into cheese.
→ Milk proteins and fats are chemically broken down and restructured by bacteria/enzymes to form cheese — a new substance.
✔ Chemical

4. We cut a piece of paper into smaller pieces.
→ Paper is still paper, just in smaller bits. No chemical reaction.
✔ Physical

5. Coal burns.
→ Burning coal produces carbon dioxide, ash, heat, and light — new substances formed.
✔ Chemical

6. Yeast makes bread rise.
→ Yeast ferments sugars to produce carbon dioxide gas (which makes bread rise) and alcohol — new substances.
✔ Chemical

7. We set our clothes to dry.
→ Water evaporates from clothes; water changes state but isn’t chemically altered.
✔ Physical

8. Fireworks
→ Fireworks involve explosions and combustion — rapid chemical reactions producing light, sound, and new gases.
✔ Chemical

9. We boil water to make tea.
→ Boiling water is a physical change (liquid to gas). Adding tea leaves may involve some chemical extraction, but the *boiling* itself is physical. The question focuses on “boil water,” so we consider that action.
✔ Physical

10. Digestion
→ Food is broken down chemically by enzymes and acids into simpler molecules (e.g., starch → sugar). New substances formed.
✔ Chemical

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✔ Final Answers for Part 1:

| Change | Physical or Chemical? |
|---------------------------------------------|------------------------|
| Liquid water freezes and becomes a solid. | Physical |
| A metal object rusts and an orange substance appears. | Chemical |
| Bacteria transforms milk into cheese. | Chemical |
| We cut a piece of paper into smaller pieces. | Physical |
| Coal burns. | Chemical |
| Yeast makes bread rise. | Chemical |
| We set our clothes to dry. | Physical |
| Fireworks | Chemical |
| We boil water to make tea. | Physical |
| Digestion | Chemical |

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## Part 2: What chemical change is it?

Match each image to the correct type of chemical change.

Image 1: Lit candle

→ Candle burning is combustion — wax reacts with oxygen to produce CO₂, water vapor, heat, and light.
✔ Combustion

Image 2: Cut apple turning brown

→ Exposure to air causes enzymes to react with oxygen — this is oxidation (natural).
✔ Oxidation (natural)

Image 3: Yogurt or cheese (fermented dairy)

→ Bacteria ferment lactose (milk sugar) into lactic acid — this is fermentation.
✔ Fermentation

Image 4: Rusty nails

→ Iron reacts with oxygen and moisture to form iron oxide (rust). This is oxidation (rust).
✔ Oxidation (rust)

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✔ Final Matching for Part 2:

- Candle → Combustion
- Brown apple → Oxidation (natural)
- Yogurt/Cheese → Fermentation
- Rusty nails → Oxidation (rust)

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## 🎯 Summary:

You’ve now correctly identified all physical vs. chemical changes and matched real-life examples to their specific types of chemical reactions. Great job!

Let me know if you’d like a printable version or flashcards for review!