Thermal Decomposition

To understand thermal decomposition, let’s break down the two words that make it up. “Thermal” refers to the application of heat, while “decomposition” refers to the breaking down of a compound into simpler components.

In a thermal decomposition reaction, heat is applied to a single reactant, causing it to break down into multiple products. This process is different from other types of reactions, “such as combustion or neutralisation, where two or more reactants combine to form one or more products.

The diagram below shows the apparatus used for thermal decomposition reactions.

Many metal carbonates can take part in thermal decomposition reactions. For example, copper carbonate decomposes to form copper oxide and carbon dioxide.

Copper carbonate Copper oxide + Carbon dioxide

The symbol equation for this reaction is:

CuCO3 (s)  CuO (s) + CO2 (g)

  • As you can see, there is only one reactant (copper carbonate)

In this reaction, copper carbonate is heated in a test tube. This will result in the release of carbon dioxide gas and copper oxide solid will remain in the test tube.


Calcium carbonate can also undergo thermal decomposition to form calcium oxide and carbon dioxide.

Calcium carbonate Calcium oxide + Carbon dioxide

Otherwise written as:

CaCO3 (s)  CaO (s) + CO2 (g)

Here, calcium carbonate decomposes to form calcium oxide and carbon dioxide.

In this reaction, copper carbonate is heated in a test tube. This results in the release of carbon dioxide gas, while solid copper oxide remains in the test tube.

Decomposition

A decomposition reaction is a type of reaction. The name doesn’t include ‘thermal’, which means that the reaction may not involve heat. In such reactions, the compound breaks down spontaneously, without the need for external heat.

An example of a decomposition reaction is hydrogen peroxide breaking down to form hydrogen and oxygen.

Hydrogen peroxide Oxygen + Water

The symbol equation for this reaction is:

2H2O2O2 + 2H2O