The energy is required to break a mole of molecules into their component atoms.
The energy is used to break bonds that come from heat whether the reaction is exothermic or endothermic.
Energy phenomena during the bond break:
The bond-breaking process absorbs energy, which is known as the endothermic process.
When an atom is split into parts, its entropy rises, implying that the split molecules have more entropy than a single atom and can move independently.
For example, breaking a hydrogen molecule requires energy, and the two split hydrogen atoms have higher energy content and are more unstable than a single hydrogen atom.