IB Chemistry - Energetics

IB Chemistry home > Syllabus 2025 > Energetics > Bond Energy

Atoms are held together in covalent compounds by forces, which we call chemical bonds. Breaking these bonds requires energy and conversely energy is released in the form of heat when they are made.

The bond energy can be defined in terms of a specific bond or more generally as an average. This section examines the usefulness of each definition.

Syllabus reference

Reactivity 1.2.1 - Bond-breaking absorbs and bond-forming releases energy.

  • Calculate the enthalpy change of a reaction from given average bond enthalpy data.


  • Include explanation of why bond enthalpy data are average values and may differ from those measured experimentally.
  • Average bond enthalpy values are given in the data booklet.

Tools and links

In Chapter 4.4