Skip to main content

Bond Dissociation Energies — Common Chemical Bonds

Bond Bond Type Bond Energy (kJ/mol) Bond Length (pm) Category
H—HSingle43674H bonds
H—FSingle56892H–Halogen
H—ClSingle431127H–Halogen
H—BrSingle366141H–Halogen
H—ISingle298161H–Halogen
H—OSingle46396H bonds
H—SSingle363134H bonds
H—NSingle391101H bonds
H—CSingle413109H bonds
C—CSingle348154C bonds
C=CDouble614134C bonds
C≡CTriple839120C bonds
C—NSingle293147C bonds
C=NDouble615129C bonds
C≡NTriple891116C bonds
C—OSingle360143C bonds
C=ODouble743123C bonds
C=O (in CO₂)Double799116C bonds
C—SSingle272182C bonds
C—FSingle485135C–Halogen
C—ClSingle339177C–Halogen
C—BrSingle276194C–Halogen
C—ISingle238214C–Halogen
N—NSingle163145N bonds
N=NDouble418125N bonds
N≡NTriple941110N bonds
N—OSingle201140N bonds
N=ODouble607121N bonds
O—OSingle146148O bonds
O=ODouble498121O bonds
O—FSingle190142O bonds
S—SSingle266205S bonds
S=ODouble523143S bonds
S—HSingle363134S bonds
F—FSingle155142Halogen bonds
Cl—ClSingle242199Halogen bonds
Br—BrSingle193228Halogen bonds
I—ISingle151267Halogen bonds
Si—OSingle452161Other
Si—CSingle318185Other
P—OSingle335163Other
P=ODouble544150Other

Values are gas-phase averages and refer to homolytic dissociation: A-B → A• + B•. The same bond type can deviate noticeably with environment — the C=O in carbonyl compounds is about 743 kJ/mol but in CO2 it's about 799 kJ/mol because of resonance stabilization in the latter. Successive bond cleavages also differ from the average: H-OH is 497 kJ/mol but the second O-H in HO• is only 428 kJ/mol. Use these for quick ΔH estimates in gas-phase reactions; for solution chemistry, factor in solvation enthalpies separately. Sources: CRC Handbook, Atkins, Zumdahl.

Frequently Asked Questions

How do you use bond energies to estimate enthalpy changes?
Sum the BDEs of every bond broken in the reactants, sum the BDEs of every bond formed in the products, then subtract: ΔH ≈ Σ(bonds broken) − Σ(bonds formed). Breaking costs energy (positive); forming releases energy (negative). For combustion of methane, you break 4 C-H plus 2 O=O and form 2 C=O plus 4 O-H — the formed bonds are stronger overall, so ΔH comes out negative. Expect ±10-50 kJ/mol error from the gas-phase averaging; for tighter numbers, work from standard heats of formation instead.
Why is the N≡N triple bond so strong?
Three shared electron pairs give N≡N about 941 kJ/mol — one of the strongest bonds catalogued. That's the kinetic floor under nitrogen chemistry: N2 makes up 78% of the atmosphere yet sits inert at room temperature, and any reaction that converts it to NH3 or NO has to pay that activation cost up front. Industrial Haber-Bosch handles it with iron catalysts at ~450 °C and 200 atm; biological nitrogen fixation uses nitrogenase, which routes around the kinetic barrier with an ATP-driven multi-electron transfer at iron-molybdenum cofactor sites.
Why are bond energies listed as averages?
The same bond type doesn't have a single fixed energy — it depends on what's attached to it. Breaking the first O-H in water takes 497 kJ/mol; breaking the second O-H in the resulting hydroxyl radical takes only 428. Tabulated values are arithmetic averages over many parent molecules, useful for ranking and for ΔH estimates within ±10-50 kJ/mol. When you need accuracy for a specific compound, look up its measured bond enthalpy directly rather than relying on the average — or use standard heats of formation, which already encode the molecule-specific environment.