Let's go through each of the 15 changes listed in the worksheet and determine whether each is a
physical change or a
chemical change. Here's how we can distinguish between them:
🔬 Definitions:
-
Physical Change: A change in which the substance’s form or state changes, but
no new substances are formed. The chemical composition remains the same.
- Examples: Melting, freezing, cutting, dissolving, crushing.
-
Chemical Change: A change in which
new substances are formed due to a chemical reaction. There is a change in the chemical composition.
- Examples: Rusting, burning, digestion, tarnishing.
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Now, let's analyze each item:
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1)
Melting of an ice cube
→ Ice turns into water (solid → liquid), but it's still H₂O.
✔ Physical Change
2)
Rusting of an iron nail
→ Iron reacts with oxygen to form iron oxide (rust). New substance formed.
✔ Chemical Change
3)
Burning of a piece of paper
→ Paper combusts, producing ash, smoke, CO₂, etc. New substances formed.
✔ Chemical Change
4)
Cutting a piece of paper
→ Size changes, but paper is still paper. No new substance.
✔ Physical Change
5)
Boiling water
→ Water turns into steam (liquid → gas), but still H₂O.
✔ Physical Change
6)
Baking a cake
→ Ingredients undergo chemical reactions (e.g., proteins denature, starches gelatinize). New substances formed.
✔ Chemical Change
7)
Breaking a glass
→ Shape changes, but glass is still glass. No new substance.
✔ Physical Change
8)
Tarnishing of silver
→ Silver reacts with sulfur in air to form silver sulfide (darkening). New substance.
✔ Chemical Change
9)
Dissolving sugar in water
→ Sugar molecules disperse in water, but no chemical reaction occurs. Can be reversed by evaporation.
✔ Physical Change
10)
Mixing baking soda and vinegar
→ Produces carbon dioxide gas, water, and sodium acetate. Bubbles form – evidence of a reaction.
✔ Chemical Change
11)
Freezing water into ice cubes
→ Liquid water becomes solid ice. Still H₂O.
✔ Physical Change
12)
Crushing a can
→ Shape changes, but aluminum is still aluminum.
✔ Physical Change
13)
Digesting food in your stomach
→ Food is broken down chemically (enzymes break bonds). New substances (nutrients) are formed.
✔ Chemical Change
14)
Ripping a piece of cloth
→ Size and shape change, but material remains the same.
✔ Physical Change
15)
Combining hydrogen and oxygen to form water
→ H₂ + O₂ → H₂O. This is a combustion reaction forming a new compound.
✔ Chemical Change
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✔ Final Answers:
1) Physical
2) Chemical
3) Chemical
4) Physical
5) Physical
6) Chemical
7) Physical
8) Chemical
9) Physical
10) Chemical
11) Physical
12) Physical
13) Chemical
14) Physical
15) Chemical
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💡
Tip for Students: Look for clues like:
- Color change
- Gas production
- Formation of precipitate
- Odor change
- Irreversibility
These often indicate a
chemical change.
Let me know if you'd like this turned into a printable answer key!
Parent Tip: Review the logic above to help your child master the concept of physical changes and chemical changes worksheet.
