Thermal Decomposition of Metal Carbonates — Gases in the Atmosphere | IGCSE Chemistry

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 5% of your exam marks.

stable

Rare

Stable5%

Air composition, greenhouse effect and climate implications appear in most series.

Thermal decomposition is a reaction in which a single compound breaks down into two or more simpler products when heated
Metal carbonates from the lower half of the reactivity series break down readily on heating to give the metal oxide plus carbon dioxide
General equation:

metal carbonate → metal oxide + carbon dioxide

ZnCO₃(s) → ZnO(s) + CO₂(g) (the white solid turns yellow when hot and back to white once cool)
CaCO₃(s) → CaO(s) + CO₂(g) (the same reaction used industrially to make lime from limestone)
Group 1 carbonates (Na₂CO₃, K₂CO₃) do not decompose at Bunsen-burner temperatures because their carbonates are very stable