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One common reaction of any metal carbonates is known as thermal decomposition. When metal carbonates are heated, they break down to form the metal oxide and carbon dioxide gas. Here are some examples.

sodium carbonate → sodium oxide + carbon dioxide

Na₂CO₃(s) → Na₂O(s) + CO₂(g)

copper(II) carbonate → copper(II) oxide + carbon dioxide

CuCO₃(s) → CuO(s) + CO₂(g)

The difficulty of this decomposition reaction depends on the reactivity of the metal in the metal carbonate. If we take the two examples above, sodium is a very reactive metal. This means that sodium carbonate is very stable and requires a high temperature to decompose. However, copper is a very unreactive metal, which is why it is useful for making water pipes, and so copper(II) carbonate is quite unstable and decomposes at a relatively low temperature.

The stability of the metal carbonates can be related to the reactivity series of metals. The higher up the series a metal is, the more reactive the metal is and so the more stable the metal carbonate is.

The stability of the metal carbonates can be measured by heating the carbonate and bubbling the carbon dioxide given off through limewater. The quicker the limewater becomes milky, the greater the rate of decomposition of the carbonate (meaning the carbonate is less stable).