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Each mole of CO 2 (44 g) reacts with one mole of calcium hydroxide (74 g) and produces one mole of water (18 g). The reaction can be considered as a strong-base-catalysed, water-facilitated reaction. [5] The reaction mechanism of carbon dioxide with soda lime can be decomposed in three elementary steps:
Carbonatation is a slow process that occurs in concrete where lime (CaO, or Ca(OH) 2 ) in the cement reacts with carbon dioxide (CO 2) from the air and forms calcium carbonate. The water in the pores of Portland cement concrete is normally alkaline with a pH in the range of 12.5 to 13.5.
This is accomplished by heating the material to above 825 °C (1,517 °F), [6] [7] a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO 2), leaving quicklime behind. This is also one of the few chemical reactions known in prehistoric times. [8] CaCO 3 (s) → CaO(s) + CO 2 (g)
Rotary lime kiln (rust-colored horizontal tube at right) with preheater, Wyoming, 2010 Traditional lime kiln in Sri Lanka. A lime kiln is a kiln used for the calcination of limestone (calcium carbonate) to produce the form of lime called quicklime (calcium oxide). The chemical equation for this reaction is: CaCO 3 + heat → CaO + CO 2
Pure lime is soluble in water containing carbonic acid, a natural, weak acid which is a solution of carbon dioxide in water and acid rain so it will slowly wash away, but this characteristic also produces autogenous or self-healing process where the dissolved lime can flow into cracks in the material and be redeposited, automatically repairing ...
Rain water contains dissolved carbon dioxide taken from the atmosphere. Some of the dissolved carbon dioxide reacts with the water to form carbonic acid, which remains in solution. Minerals containing calcium and magnesium form soluble bicarbonates when exposed to carbonic acid. Water containing these minerals is known as "hard water".
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The carbon dioxide combines with water or water vapor to produce a weak carbonic acid: CO 2 + H 2 O –> H 2 CO 3. This reacts with the hydroxides to produce carbonates and water in an exothermic reaction. [ 6 ]