What processes occur throughout the limestone cycle? (3 marks)
The naturally occurring compound in limestone is calcium carbonate (CaCO3). When heated, the CaCO3 thermally decomposes (is broken down by the heat in an endothermic process) to produce calcium oxide (CaO) and carbon dioxide (CO2). Calcium oxide is also known as "quicklime" and this reaction can be summarised by the equation: CaCO3 --> CaO + CO2. CaO then reacts with water (H2O) to form calcium hydroxide (Ca(OH)2). This reaction can be summarised by: CaO + H2O --> Ca(OH)2. It is important to note that Ca(OH)2 is a solid at this point, but dissolves in excess water to produce limewater, with the same chemical formula: Ca(OH)2. Limewater can be used to test for carbon dioxide (CO2), as this reaction produces CaCO3, which is insoluble in water. This reaction can be summarised by: Ca(OH)2 + CO2 --> CaCO3 + H2O.All these reactions summarise the limestone cycle.
