Essay - Types of Chemical Weathering

Q. Discuss two types of chemical weathering

* Focus on carbonation & hydration and hydrolysis *

Carbonation

• One of the most common forms of chemical weathering

• Rainwater mixes with carbon dioxide in the atmosphere to form a weak carbonic acid (acid rain).

• The acid reacts with certain minerals in the rocks

• This forces the rocks to decompose

• Rocks such as limestone with high levels of calcium carbonate are very susceptible to carbonation.

• The carbonic acid reacts with the calcium carbonate to form calcium bicarbonate.

• This is then dissolved by more rain water before it is removed in solution.

• If examined closely, you can see the chemical reaction as a white fizzing foam.

• E.g. The Burren

• H2O + CO2 = H2CO3 ——-(water + carbon dioxide = carbonic acid)

• H2C03 + CaCO3 = Ca(HCO3)2 —— (carbonic acid + calcium carbonate = calcium bicarbonate)

Hydration and hydrolysis

• Hydration and hydrolysis are two separate distinct processes, however, they both result from the same action; the addition of water to minerals in a rock.

• Hydration = water is absorbed by minerals that do not contain water, forcing the minerals to expand and the rock to swell.

• The increased pressure places strain on the rock, eventually forcing it to shatter.

• Most prominent in rocks with a high clay content.

• Hydrolysis = the process whereby hydrogen in water reacts with minerals in the rock.

• This triggers a series of chemical changes.

• Minerals resistant to hydrolysis will slowly result in the rock crumbling.