Chemical Weathering

Question 1

What is chemical weathering?

Answer 1

• breaking down of rocks caused by chemical reactions

Question 2

What is the key medium for chemical weathering?

Answer 2

• water

Question 3

Where is chemical weathering most effective?

Answer 3

• below surface where percolating water has pilled up organic acids

Question 4

What are the diff types of chemical weathering?

Answer 4

• hydrolysis
• hydration
• carbonation/solution

Question 5

What is hydrolysis?

Answer 5

• breaking down of rock when it reacts w water
• e.g. occurs in rocks containing orthoclase feldspar
  • when feldspar reacts w rainwater it forms Kaolinite
  • acid + hydroxyl removed in solution, leaving Kaolinite

Question 6

What is hydration?

Answer 6

• when minerals absorb water, expand + change
• e.g. anhydrite changed to gypsum + expands by 0.5%

CaSO4 ➡️ CaSO4.2H20

• some shales can expand up to 1600%

Question 7

What is carbonation?

Answer 7

• [1] rainfall w dissolved CO2 forms a carbonic acid which [2] reacts w CaCO3 to form calcium bicarbonate which is soluble + is washed away

[1] H20 + CO2 ➡️ H2CO3
[2] H2CO3 + CaCO3 ➡️ Ca(HCO3)2

• occurs on rocks w CaCO3 (e.g. limestone + chalk)