Physical or chemical changes? worksheet - Free Printable

Let's solve the problem step by step.

---

Part 1: Identify whether each change is physical or chemical

We need to determine if each process involves a physical change (no new substance formed, only state or form changes) or a chemical change (new substances are formed due to chemical reactions).

| Change | Physical or Chemical? |
|-------|------------------------|
| Liquid water freezes and becomes a solid. | Physical – Only a change in state (liquid → solid), no new substance formed. |
| A metal object rusts and an orange substance appears. | Chemical – Rusting is oxidation, forming iron oxide (a new substance). |
| Bacteria transforms milk into cheese. | Chemical – Fermentation by bacteria changes milk proteins and lactose into cheese; new substances are formed. |
| We cut a piece of paper into smaller pieces. | Physical – Only size changes; no new substance. |
| Coal burns. | Chemical – Combustion produces carbon dioxide, ash, etc. New substances formed. |
| Yeast makes bread rise. | Chemical – Yeast ferments sugars to produce CO₂ gas, causing dough to rise. This is fermentation. |
| We set our clothes to dry. | Physical – Water evaporates from clothes; it’s a phase change (liquid → gas). No new substance. |
| Fireworks | Chemical – Explosion involves combustion and chemical reactions producing light, sound, and color. |
| We boil water to make tea. | Physical – Boiling water is a phase change (liquid → gas). The water itself doesn't chemically change (though tea extraction may involve some chemical processes, boiling water is primarily physical). |
| Digestion | Chemical – Food is broken down into simpler molecules (e.g., proteins → amino acids) via enzymes; new substances are formed. |

---

Part 2: Match images to chemical changes

Now, match each image with the correct type of chemical change:

1. Candle burning
→ Combustion
*Explanation:* Burning wax is a combustion reaction where hydrocarbons react with oxygen to produce CO₂, water vapor, and light/heat.

2. Cut apple turning brown
→ Oxidation (natural)
*Explanation:* When apple flesh is exposed to air, enzymes cause browning due to oxidation of phenolic compounds.

3. Yogurt or fermented dairy
→ Fermentation
*Explanation:* Lactic acid bacteria convert lactose into lactic acid, changing the texture and taste — this is fermentation.

4. Rusty nails
→ Oxidation (rust)
*Explanation:* Iron reacts with oxygen and moisture to form iron oxide (rust), which is a classic example of oxidation.

---

✔ Final Answers

#### Table: Physical or Chemical Changes

| 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 |

#### Image Matching

- Candle → Combustion
- Apple (browning) → Oxidation (natural)
- Yogurt → Fermentation
- Rusty nails → Oxidation (rust)

---

🔍 Summary:

- Physical changes: Involve changes in state, shape, or size without altering chemical composition.
- Chemical changes: Involve breaking/forming bonds, creating new substances.
- The examples show common real-life instances of both types, helping distinguish them clearly.

Let me know if you'd like a printable version or further explanations!