Can someone explain the explanation:
Decomposition is generally an endothermic process; energy is absorbed by the reactants during the reaction. Generally, you must apply energy to make the process happen.
Decomposition is the process by which organic substances are broken down into simpler forms of matter. Decomposition may be abiotic, or chemical and biotic (biodegradation or rotting). The former means degradation of a substance by chemical or physical processes, e.g. thermal decomposition of calcium carbonate, sodium azide or hydrogen peroxide:
CaCO3 → CaO + CO2
2NaN3 → 2Na + 3N2
2H2O2 → 2H2O + O2
Biotic decomposition means the metabolic breakdown of materials into simpler components by living organisms, typically by microorganisms like bacteria, fungus or earthworms. In either of the cases simpler and smaller molecules or elements are formed from larger, more complex reactants.
Molecules are formed by sharing of electrons between atoms. When these bonds are broken, energy is always required to be input. Bond breaking is always endothermic, so is the process of decomposition.