What is bond energy?
Bond energy (or bond enthalpy) is the average energy needed to break one mole of a particular type of chemical bond in the gas phase. Breaking bonds always requires energy input, while forming new bonds always releases energy.
How this calculator works
Using Hess’s law applied to average bond energies, the enthalpy change of a reaction can be estimated as:
ΔH(reaction) ≈ Σ(bond energies broken) − Σ(bond energies formed)
Add up the average bond energies of every bond broken in the reactants, add up the average bond energies of every bond formed in the products, and enter each total. The calculator subtracts them to give the overall estimated enthalpy of reaction. A negative result means the reaction is exothermic (releases energy, more energy was released forming bonds than was used breaking them); a positive result means it’s endothermic (absorbs energy overall).
Because average bond energies are approximations that vary somewhat between molecules, this method gives a useful estimate rather than an exact value — it’s most accurate for simple gas-phase reactions. This tool is for general chemistry education purposes.