Average Bond Energies
Average bond energies (kJ/mol) for single, double, and triple bonds, with bond lengths for the carbon multiple-bond ladders. Estimate a reaction enthalpy from bond energies: ΔH ≈ Σ D(bonds broken) − Σ D(bonds formed).
| Bond | Bond Order | Bond Energy (kJ/mol) | Bond Length (Å) |
|---|---|---|---|
| H–H | Single | 436 | — |
| C–S | Single | 260 | — |
| F–Cl | Single | 255 | — |
| H–C | Single | 415 | — |
| C–Cl | Single | 330 | — |
| F–Br | Single | 235 | — |
| H–N | Single | 390 | — |
| C–Br | Single | 275 | — |
| Si–Si | Single | 230 | — |
| H–O | Single | 464 | — |
| C–I | Single | 240 | — |
| Si–P | Single | 215 | — |
| H–F | Single | 569 | — |
| N–N | Single | 160 | — |
| Si–S | Single | 225 | — |
| H–Si | Single | 395 | — |
| N=N | Double | 418 | — |
| Si–Cl | Single | 359 | — |
| H–P | Single | 320 | — |
| N≡N | Triple | 946 | — |
| Si–Br | Single | 290 | — |
| H–S | Single | 340 | — |
| N–O | Single | 200 | — |
| Si–I | Single | 215 | — |
| H–Cl | Single | 432 | — |
| N–F | Single | 270 | — |
| P–P | Single | 215 | — |
| H–Br | Single | 370 | — |
| N–P | Single | 210 | — |
| P–S | Single | 230 | — |
| H–I | Single | 295 | — |
| N–Cl | Single | 200 | — |
| P–Cl | Single | 330 | — |
| C–C | Single | 345 | 1.54 |
| N–Br | Single | 245 | — |
| P–Br | Single | 270 | — |
| C=C | Double | 611 | 1.34 |
| O–O | Single | 140 | — |
| P–I | Single | 215 | — |
| C≡C | Triple | 837 | 1.20 |
| O=O | Double | 498 | — |
| S–S | Single | 215 | — |
| C–N | Single | 290 | 1.43 |
| O–F | Single | 160 | — |
| S–Cl | Single | 250 | — |
| C=N | Double | 615 | 1.38 |
| O–Si | Single | 370 | — |
| S–Br | Single | 215 | — |
| C≡N | Triple | 891 | 1.16 |
| O–P | Single | 350 | — |
| Cl–Cl | Single | 243 | — |
| C–O | Single | 350 | 1.43 |
| O–Cl | Single | 205 | — |
| Cl–Br | Single | 220 | — |
| C=O | Double | 741 | 1.23 |
| O–I | Single | 200 | — |
| Cl–I | Single | 210 | — |
| C≡O | Triple | 1080 | 1.13 |
| F–F | Single | 160 | — |
| Br–Br | Single | 190 | — |
| C–F | Single | 439 | — |
| F–Si | Single | 540 | — |
| Br–I | Single | 180 | — |
| C–Si | Single | 360 | — |
| F–P | Single | 489 | — |
| I–I | Single | 150 | — |
| C–P | Single | 265 | — |
| F–S | Single | 285 | — |
Important Notes
- These are AVERAGE values over many compounds — bond-energy estimates of ΔH are approximations; enthalpies of formation give exact values when available.
- ΔH ≈ Σ D(bonds broken) − Σ D(bonds formed). Breaking bonds costs energy (positive); forming bonds releases it.
- For the same pair of atoms, more bonds = stronger and shorter: C–C 345 kJ/mol (1.54 Å) → C=C 611 (1.34 Å) → C≡C 837 (1.20 Å).
- Bond lengths are tabulated for the carbon single/double/triple ladders (C–C, C–N, C–O); a dash means the source does not tabulate a length for that bond.
- ChemWhiz problems that need bond energies supply them in the problem statement; this table is the general reference.
Source: OpenStax Chemistry 2e, §7.5 Strengths of Ionic and Covalent Bonds (Tables 7.2 and 7.3) (CC BY 4.0)