---
title: "Chemical versus physical weathering; factors"
subject: "Engineering Geology I"
chapter: 6
key: "semester_3/engineering_geology_i:chemical-versus-physical-weathering-factors"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/chemical-versus-physical-weathering-factors
site: BCT Engineering
---

# Chemical versus physical weathering; factors

Engineering Geology I · Chapter 6: Physical Geology

- Asked in: 2080 Bhadra, 4 marks
- Video: [Earth Science - Types of Weathering](https://www.youtube.com/watch?v=ZM4M2J3GdSQ) — Michael DiPasquale (Mr. D)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/chemical-versus-physical-weathering-factors
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-6

## Question

Differentiate between chemical and physical weathering. What are the factors of weathering of rocks?

## Short answer

Physical weathering mechanically breaks rocks without mineral change (frost wedging, exfoliation), while chemical weathering alters minerals via solution, hydrolysis and oxidation. Factors are climate, rock type and structure, topography, vegetation and time.

## Answer

| Point | Physical weathering | Chemical weathering |
|---|---|---|
| Change | Rock breaks into pieces; minerals unchanged | Minerals change to new minerals |
| Main agents | Temperature, frost, pressure release, roots | Water, CO$_2$, oxygen, acids |
| Favoured by | Cold or dry climates, steep slopes | Warm, humid climates |
| Processes | Frost wedging, exfoliation, thermal stress | Solution, hydrolysis, oxidation, carbonation |
| Products | Angular fragments, sand | Clay, oxides, soluble salts |
| Link between them | Increases the surface area, which speeds up chemical weathering | Weakens the rock, which helps it break up physically |

#### Factors of weathering
1. **Climate:** temperature and rainfall. Frost action dominates in cold areas; chemical weathering in hot, humid areas.
2. **Rock type and mineral composition:** quartz is very resistant; olivine, feldspar and calcite weather quickly.
3. **Rock structure:** joints, bedding and faults let water and air enter.
4. **Topography (relief):** steep slopes remove debris and expose fresh rock; gentle slopes keep a thick soil cover.
5. **Vegetation and organisms:** roots, bacteria and humic acids speed up weathering, but dense cover also protects the surface.
6. **Time:** the longer the exposure, the deeper the weathering.
7. **Grain size and porosity:** coarse or porous rocks have more surface for reaction.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Chemical weathering differs from physical because it:
   A. Changes minerals to new minerals
   B. Only breaks rock
   C. Needs frost
   D. Occurs only in deserts
   Answer: A. Physical keeps minerals unchanged. (Key point: Difference)

2. Physical weathering is favoured by:
   A. Warm humid climates
   B. Cold, dry climates and steep slopes
   C. Tropical forests
   D. Wet lowlands
   Answer: B. Chemical is favoured by warm humid climates. (Key point: Climate)

3. Chemical weathering products are:
   A. Angular fragments
   B. Gravel only
   C. Clay, oxides, soluble salts
   D. Moraines
   Answer: C. Physical yields angular fragments and sand. (Key point: Products)

4. Rock structure affects weathering because:
   A. They block water
   B. They add minerals
   C. They cool the rock
   D. Joints, bedding and faults let water and air in
   Answer: D. Openings admit agents. (Key point: Rock structure)

5. Dense vegetation:
   A. Speeds weathering through roots and acids but also protects the surface
   B. Only speeds weathering
   C. Only protects
   D. Has no effect
   Answer: A. Both effects occur. (Key point: Vegetation)

## Related in Engineering Geology I

- [Physical and chemical weathering](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aphysical-and-chemical-weathering) — Engineering Geology I, chapter 6, asked 5×
- [Volcanism; chemical weathering](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Avolcanism-chemical-weathering) — Engineering Geology I, chapter 6
- [Define weathering and its controlling factors](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Adefine-weathering-and-its-controlling) — Engineering Geology I, chapter 6, asked 4×
- [Weathering versus erosion](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aweathering-versus-erosion) — Engineering Geology I, chapter 6, asked 5×
- [Intrusive versus extrusive igneous rocks](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aintrusive-versus-extrusive-igneous-rocks) — Engineering Geology I, chapter 4, asked 3×

## Related in other subjects

- [Physical and chemical disintegration](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aphysical-chemical-disintegration) — Soil Mechanics, chapter 1
- [Physical and chemical causes of deterioration](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aphysical-chemical-causes-deterioration) — Concrete Technology and Masonry Structure, chapter 6, asked 5×
- [Physical and chemical characteristics of solid waste](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Asolid-waste-characteristics) — Environment and Pollution Control, chapter 5