2. H2O + CO2 H2CO3 H2CO3 (HCO3)- + H+ 1. Rainwater acidifies.
The chemical reactions that make karst modelling possible are explained below.
1. Rainwater acidifies.
CO2 from the atmosphere dissolves in rainwater and reacts with it to form carbonic acid.
H2O + CO2
H2CO3
The dissolved carbonic acid partially dissociates and forms the bicarbonate ion, which is dissolved in the rain water. Under these conditions, the water is acidic and can react with limestone.
H2CO3
(HCO3)- + H+

3. CaCO3 + (HCO3)- + H+ (HCO3)2Ca (HCO3)2Ca 2(HCO3)- + Ca2+
The chemical reactions that make karst modelling possible are explained below.
2. The acidified water reacts with the limestone and dissolves it.
The limestone (calcium carbonate), which is insoluble in water, is attacked by the bicarbonate ion dissolved in the rainwater. This transforms the calcium carbonate into calcium bicarbonate, which is soluble in water.
CaCO3 + (HCO3)- + H+
(HCO3)2Ca
This immediately produces dissolved calcium bicarbonate in the water, which seeps through the fissures in the limestone, which is loaded with this substance.
(HCO3)2Ca
2(HCO3)- + Ca2+

4. (HCO3)2Ca CaCO3 + H2O + CO2 3. Simplified chemical reaction.
The chemical reactions that make karst modelling possible are explained below.
3. Simplified chemical reaction.
All the chemical processes above can be summarised in the following equilibrium between two reverse chemical reactions:
CaCO3 + H2O + CO2
(HCO3)2Ca
Limestone
(calcium carbonate)
Calcium bicarbonate
• The reaction that makes limestone transform into bicarbonate and dissolve in water.
• The reaction that makes bicarbonate transform back into limestone, which precipitates (separates as a solid) because it is not soluble.

5. (HCO3)2Ca CaCO3 + H2O + CO2 In summary:
When the equilibrium is shifted to the right, the water dissolves the limestone mass, increasing the size of the cracks and fissures.
CaCO3 + H2O + CO2
(HCO3)2Ca

6. (HCO3)2Ca CaCO3 + H2O + CO2 In summary:
When the equilibrium is shifted to the left, calcium carbonate (limestone) is produced again, which precipitates in the form of stalactites and stalagmites.
CaCO3 + H2O + CO2
(HCO3)2Ca