Chemical Weathering

Question:

Describe the agents and processes involved in the chemical decomposition of rocks. Which of the processes you identified is likely to be most effective in eroding a terrain composed mainly of limestone, and why?

ESSAY

Weathering is the disintegration of rocks in ‘situ’ meaning at original place of rest, into smaller particles. The decomposition of rocks by altering the mineral composition of the rock is represented by the term chemical Weathering, water is a dominant agent in this process. This is where different processes are responsible for the breaking down of rocks and various minerals. These processes more likely occur at the surface of rocks and minerals. There are (5) processes associated with weathering: • Hydration• Hydrolysis• Oxidation / reduction• Carbonation and • Complexation. These processes give us a clearer view on the huge topic of weathering.

Hydration is basically a reaction of a substance with water in the form of H2O molecules. Rocks containing salt minerals absorb water into their structure, these allow them to swell and become vulnerable to be broken down in the future. Gypsum is an excellent example of water being added to anhydrite (CaSO4). So we could therefore say that hydration is a physiochemical process in which the rocks may swell and exert pressure and by also changing their structure chemically. Other examples of hydrates are Glauber’s salt (sodium sulfate decahydrate, Na2SO4∙10H2O); washing soda (sodium carbonate decahydrate, Na2CO3∙10H2O); borax (sodium tetraborate decahydrate, Na2B4O7∙10H2O); the sulfates known as vitriols (e.g., Epsom salt, MgSO4∙7H2O); and the double salts known collectively as alums (M+2SO4∙M+32(SO4)3∙24H2O, where M+ is a monopositive cation, such as K+or NH4+, and M3+ is a tripositive cation, such as Al3+ or Cr3+). These are just a few examples illustrating hydration.

Hydrolysis is another chemical process of weathering; this is one of the most important in the decomposition of rocks and the...