What do average bond enthalpies represent?

Average bond enthalpies represent average values for the energies required to break similar bonds. This means that they provide a general estimate of the energy needed to break a particular type of bond (like C-H, O-H, or N-H) across various compounds, rather than specific values for every instance of that bond in every molecule.

In practice, bond enthalpies are averaged because the energy required to break a bond can vary depending on the molecular environment surrounding the bond. By using average bond enthalpies, chemists can make predictions about the energy changes during chemical reactions without needing to measure or calculate the precise energy for every individual bond in every molecule involved. This simplification is particularly useful for estimating reaction enthalpies based on bond formation and breaking.