The word equation for the reaction that you presented is:
Aqueous calcium hydroxide reacts with gaseous carbon dioxide to produce solid calcium carbonate plus liquid water.
`~Ca(OH)_2(aq) + ~CO_2(g) -gt ~CaCO_3(s) + ~H_2O(l)`
But, the reaction is more complicated than it appears. When carbon dioxide gas is added to aqueous calcium hydroxide, the carbon dioxide reacts with the water in the aqueous calcium hydroxide to form carbonic acid:
`~CO_2(g) + H_2O(l) harr ~H_2CO_3(aq)`
The carbonic acid then reacts with the calcium hydroxide to form calcium carbonate and water:
` ~Ca(OH)_2(aq) + ~H_2CO_3(aq)harr~CaCO_3(s) + 2H_2O(l)`
The word equation for this reaction is: Aqueous calcium hydroxide reacts with aqueous carbonic acid to produce solid calcium carbonate plus liquid water.
The reaction between calcium hydroxide and carbonic acid can be classified as a double replacement reaction. The reaction is also an acid base reaction.