Let's solve this step by step. The task is to identify whether each of the listed changes is a
chemical change or a
physical change.
Definitions:
-
Chemical Change: A change where new substances are formed due to a chemical reaction. The molecular composition changes.
-
Physical Change: A change in form (like state, shape, size) but
no new substances are formed. The substance’s identity remains the same.
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Now let's go through each item:
1.
Heating water into steam
→ Water changes from liquid to gas, but it's still H₂O. No new substance formed.
✔ Physical Change
2.
Milk going sour
→ Caused by bacterial action that converts lactose into lactic acid. New substances form (lactic acid).
✔ Chemical Change
3.
Dissolving sugar in water
→ Sugar molecules disperse in water but remain as sugar. Can be recovered by evaporation.
✔ Physical Change
4.
Iron rusting
→ Iron reacts with oxygen and water to form iron oxide (rust). New substance forms.
✔ Chemical Change
5.
Hydrochloric acid and sodium hydroxide reacting and forming salt and water
→ This is a neutralization reaction: HCl + NaOH → NaCl + H₂O. New substances form.
✔ Chemical Change
6.
Digesting food into nutrients
→ Complex molecules (like proteins, carbs) are broken down into simpler ones via enzymes. Chemical bonds are broken and reformed.
✔ Chemical Change
7.
Melting ice into water
→ Solid to liquid phase change. Still H₂O.
✔ Physical Change
8.
Acid rain dripping onto limestone and making carbon dioxide gas
→ Acid (e.g., H₂SO₄ or HNO₃) reacts with calcium carbonate (CaCO₃) in limestone to produce CO₂ gas. New substances form.
✔ Chemical Change
9.
Breaking a glass into pieces
→ Only the size and shape change. Glass is still glass. No new substance.
✔ Physical Change
10.
Hydrogen peroxide decomposing into oxygen gas and water
→ 2H₂O₂ → 2H₂O + O₂. Breakdown of H₂O₂ into different substances.
✔ Chemical Change
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Final Answers:
| # | Change | Type |
|---|--------|------|
| 1 | Heating water into steam |
Physical |
| 2 | Milk going sour |
Chemical |
| 3 | Dissolving sugar in water |
Physical |
| 4 | Iron rusting |
Chemical |
| 5 | Hydrochloric acid and sodium hydroxide reacting and forming salt and water |
Chemical |
| 6 | Digesting food into nutrients |
Chemical |
| 7 | Melting ice into water |
Physical |
| 8 | Acid rain dripping onto limestone and making carbon dioxide gas |
Chemical |
| 9 | Breaking a glass into pieces |
Physical |
| 10 | Hydrogen peroxide decomposing into oxygen gas and water |
Chemical |
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✔ Summary:
-
Physical Changes: 1, 3, 7, 9
-
Chemical Changes: 2, 4, 5, 6, 8, 10
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Parent Tip: Review the logic above to help your child master the concept of chemical and physical changes worksheet.
