Bond Energy Calculator
Estimates an enthalpy change by counting bonds.
Estimated ΔH
— kJ/mol
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
Energy to break bonds — kJ/mol
Energy released forming bonds — kJ/mol
The reaction is —
Reading this —
The formula
ΔH ≈ Σ bonds broken − Σ bonds formed
Breaking bonds takes energy and forming them releases it. Count each bond in the balanced equation, including coefficients.
What to watch out for
The default values are H₂ + Cl₂ → 2HCl. Bond energies differ a little between tables, so use the ones your course gives.
Frequently Asked Questions
What is ΔH for H₂ + Cl₂ → 2HCl?
(436 + 243) − (2 × 431) = -183 kJ/mol.
Why is it broken minus formed?
The energy going in to break bonds counts as positive, and the energy coming out of new bonds as negative.