Explanation:
We are given a list of 10 weathering examples and asked to label each as either
physical (mechanical) weathering or
chemical weathering, based on the definitions:
-
Physical weathering: Breaks rocks into smaller pieces *without changing their chemical composition* (e.g., freezing/thawing, abrasion, exfoliation).
-
Chemical weathering: Changes the rock’s *chemical composition* through reactions (e.g., oxidation, hydrolysis, carbonation, acid dissolution).
Let’s go one by one:
1.
Colonies of lichens growing on the surface of rocks
→ Lichens secrete weak acids that dissolve minerals in the rock. This changes the rock chemically.
✔ Chemical
2.
The wedging of tree roots in granite rock outcrops
→ Roots grow into cracks and physically pry the rock apart. No chemical change.
✔ Physical
3.
Solution of limestone by acidic groundwater
→ Acid (like carbonic acid) dissolves calcite in limestone (CaCO₃ + H₂CO₃ → Ca²⁺ + 2HCO₃⁻). Chemical reaction.
✔ Chemical
4.
The oxidation of minerals which contain iron
→ Iron reacts with oxygen and water to form rust (e.g., hematite or limonite). Classic chemical change.
✔ Chemical
5.
Animal burrows dug in rock that let in water and air
→ Burrows themselves don’t change chemistry; they just create openings for water/air to enter — but the *act of burrowing* is physical disruption. However, the question says “Animal burrows dug in rock that let in water and air” — the key action is *digging*, which is mechanical. The letting-in of water/air is a consequence, not the weathering itself. So this is
physical (biological weathering via mechanical means).
✔ Physical
6.
Repeated freezing and thawing of water cracks rocks
→ Water expands when it freezes, cracking rock. No chemical change. Classic physical weathering.
✔ Physical
7.
The action of water, salt, and air on car fenders and parapets
→ This describes rusting/corrosion of metal (iron in steel), which is oxidation — a chemical process. Even though it's man-made, the weathering type is still chemical.
✔ Chemical
8.
Sun fading of paint on houses and cars
→ UV radiation breaks down pigments and binders in paint — this is *photodegradation*, a chemical change (bonds broken by light energy). So it’s
chemical weathering.
✔ Chemical
9.
Formation of pebbles in streams during the winter
→ Pebbles form by abrasion: rocks knock against each other in moving water, wearing them down. Physical process.
✔ Physical
10.
Lifted sections of sidewalk along tree-lined streets
→ Tree roots push up concrete slabs — mechanical force. No chemical change.
✔ Physical
Now double-check:
1. Chemical
2. Physical
3. Chemical
4. Chemical
5. Physical
6. Physical
7. Chemical
8. Chemical
9. Physical
10. Physical
All consistent.
Final Answer:
1. Chemical
2. Physical
3. Chemical
4. Chemical
5. Physical
6. Physical
7. Chemical
8. Chemical
9. Physical
10. Physical
Parent Tip: Review the logic above to help your child master the concept of physical and chemical weathering worksheet.
