For example , the reaction between hydrochloric acid and calcium carbonate ( limestone or chalk ) is depicted below : 2 HCl + CaCO 3 → CaCl 2 + H 2CO 3 The carbonic acid ( H2CO3 ) then decomposes to water and CO2 .
For example , the reaction between hydrochloric acid and calcium carbonate ( limestone or chalk ) makes carbon dioxide : The carbonic acid ( H2CO3 ) then decomposes to water and CO2 .