Work out bond enthalpy instantly with clear inputs, formula shown and shareable results.
Breaking bonds costs energy and forming bonds releases it, so a reaction's enthalpy estimated from bond enthalpies is energy in minus energy out: bonds broken minus bonds formed. When the products' bonds are collectively stronger the ratio exceeds one and the reaction is exothermic. Bond enthalpies are averages across many molecules, so this route is an estimate rather than a measurement.
Bond enthalpy route
dH = sum(bonds broken) - sum(bonds formed)
Strength ratio
ratio = energy formed / energy broken
Bond enthalpies are averaged over many compounds, so a specific molecule's bonds differ by a few tens of kJ/mol. Formation enthalpies are compound-specific and more accurate.
Poorly. Bond enthalpies are defined for gas-phase species, and solvation energies in solution are often larger than the bond differences.