Mean bond enthalpy: the definition and the sign
Dr Lavan Ganeshkumar, PhD · updated 4 October 2026
Mean bond enthalpy is the enthalpy change to break one mole of a specified bond in the gaseous state, averaged over a range of different compounds.
Words that must appear
- One mole of a specified bond
- In the gaseous state
- Averaged over a range of compounds
The sign
Breaking bonds is endothermic and making bonds is exothermic. For a reaction, delta H equals the sum of the bonds broken minus the sum of the bonds made.
Do not confuse with
The bond enthalpy in one named molecule. The mean is averaged over many compounds.
Common questions
What is mean bond enthalpy?
The enthalpy change to break one mole of a specified bond in the gaseous state, averaged over a range of different compounds.
Is breaking a bond exothermic or endothermic?
Endothermic.
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