What information will you get from the given reaction ?\[\mathrm{CaCO_{3(s)} \xrightarrow{\Delta} CaO_{(s)} + CO_{2}\uparrow}\]

Answer: On heating, calcium carbonate decomposes into calcium oxide and carbon dioxide — a thermal decomposition reaction.

• One reactant, calcium carbonate (limestone), breaks up into two products, so it is a decomposition reaction. Heat is needed, so it is a thermal decomposition.
• Calcium oxide (quicklime) is the solid left behind and carbon dioxide is given off as a gas (shown by the upward arrow).
• The carbon dioxide formed turns freshly prepared lime water milky: \(\mathrm{Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O}\). This reaction is used to prepare quicklime from limestone.