Explanation:
Let’s go through each item one by one and decide whether it’s a
chemical change or a
physical change, using the definitions given:
-
Chemical change: A reaction happens, new substances form, and energy is absorbed or released. The identity of the substance changes.
-
Physical change: The form or state changes, but the substance stays the same — no new substances are made.
1.
Heating water into steam
→ Water (liquid) turns into water vapor (gas), but it’s still H₂O. No new substance.
✔ Physical
2.
Milk going sour
→ Bacteria turn lactose into lactic acid — new substance forms, taste/smell change.
✔ Chemical
3.
Dissolving sugar in water
→ Sugar molecules spread out in water, but they’re still sugar — can be recovered by evaporation.
✔ Physical
4.
Iron rusting
→ Iron (Fe) reacts with oxygen and water to form iron oxide (rust) — new substance.
✔ Chemical
5.
Hydrochloric acid and sodium hydroxide reacting and forming salt and water
→ Classic neutralization reaction: HCl + NaOH → NaCl + H₂O. New substances formed.
✔ Chemical
6.
Digesting food into nutrients
→ Enzymes break down big molecules (like carbs, proteins) into smaller ones (sugars, amino acids) — chemical reactions.
✔ Chemical
7.
Melting ice into water
→ Solid water → liquid water. Same substance, just phase change.
✔ Physical
8.
Acid rain dripping onto limestone and making carbon dioxide gas
→ Limestone (CaCO₃) reacts with acid (H₂SO₄ or HNO₃) → CO₂ gas + other products. Gas formation = new substance.
✔ Chemical
9.
Breaking a glass into pieces
→ Still glass, just smaller pieces. No new substance.
✔ Physical
10.
Hydrogen peroxide decomposing into oxygen gas and water
→ 2H₂O₂ → 2H₂O + O₂. One substance breaks into two new ones.
✔ Chemical
Now let’s list them clearly:
1. Physical
2. Chemical
3. Physical
4. Chemical
5. Chemical
6. Chemical
7. Physical
8. Chemical
9. Physical
10. Chemical
Final Answer:
1. Physical
2. Chemical
3. Physical
4. Chemical
5. Chemical
6. Chemical
7. Physical
8. Chemical
9. Physical
10. Chemical
Parent Tip: Review the logic above to help your child master the concept of chemical change worksheet.
