Thermal decomposition is when heat causes a compound to break down into at least two chemical substances.
All substances have a decomposition temperature – the temperature at which they will chemically decompose. This temperature varies from one substance to another. Chemical decomposition means that the substance actually changes into something else. The heat breaks the chemical bonds holding together the substance’s atoms and molecules.
The reaction is endothermic. This means that heat from an external source is required to break the ionic or covalent bonds in the compound undergoing decomposition.