Answer: the addition of energy
Explanation: A decomposition reaction is one in which one reactant decomposes to produce two or more than two products.
Thus to break the bonds between the reactant molecules, energy has to be supplied. All decomposition reactions are called as endothermic reactions as all of them require energy.
For example:
[tex]CaCO_3\rightarrow CaO+CO_2[/tex]
