What is bond dissociation energy?

Bond dissociation energy (BDE) is the energy required to homolytically break one mole of a specific bond in the gas phase, producing two radical fragments. It is always positive (endothermic). Values are averages across similar environments, so they give estimates, not exact answers.

Why does this give an estimate, not an exact ΔH?

Tabulated BDE values are averages. The same bond type (e.g. C–H) has slightly different energies in different molecules. For accurate thermochemistry, use standard enthalpies of formation. BDE-based estimates are typically accurate to ±10–50 kJ/mol.

What does a negative ΔH mean?

A negative ΔH (bonds formed release more energy than bonds broken absorb) means the reaction is exothermic — energy is released to the surroundings. A positive ΔH means the reaction is endothermic — energy must be supplied.

Why are only gas-phase BDEs listed?

BDE tables are defined for gas-phase reactions. In solution, solvation effects change the apparent energies. This tool is designed for gas-phase or educational approximations only.

How do I handle a double or triple bond?

Select the bond with the correct bond order (e.g. "C=O" for a carbonyl or "C≡N" for a nitrile). Each entry in the table corresponds to a specific bond order.

Can I use this for ionic or metallic bonds?

No. BDE values apply to covalent bonds. Ionic and metallic bonding require lattice energy or cohesive energy calculations, which are outside the scope of this tool.

Bond Dissociation Energy

Name: Bond Dissociation Energy
Availability: InStock
Author: Nham Vu

Look up bond dissociation energies and estimate reaction enthalpy from bonds broken and formed.

BDE Reference Table

kJ/mol

Bond	Example	BDE

Bonds Broken (reactants)

Click "Add" next to a bond in the table to add it here.

Bonds Formed (products)

Click "Add" next to a bond, then move it here using the arrows.

Estimated Reaction Enthalpy

Σ BDE broken

kJ/mol

Σ BDE formed

kJ/mol

ΔH (approx.)

kJ/mol

Add bonds above to calculate ΔH.

ΔH ≈ Σ BDE(bonds broken) − Σ BDE(bonds formed) · Average BDE values; gas-phase approximation only.

Summary

Look up bond dissociation energies and estimate reaction enthalpy from bonds broken and formed.

How it works

Browse or search the BDE reference table to find a bond (e.g. C–H, O=O, N≡N).
Add bonds broken in the reaction using the "Bonds Broken" panel, with a count for each.
Add bonds formed in the product using the "Bonds Formed" panel, with a count for each.
The calculator sums energy in (bonds broken) and energy out (bonds formed).
ΔH ≈ Σ BDE(broken) − Σ BDE(formed) is displayed with a sign and unit label.
Positive ΔH = endothermic; negative ΔH = exothermic.

Use cases

Estimate the enthalpy of simple gas-phase reactions for introductory chemistry courses.
Cross-check textbook bond energy calculations without manual table lookups.
Quickly compare the relative stability of different bond types.
Teach students the difference between endothermic and exothermic reactions using BDE sums.
Screen candidate reaction pathways by their approximate energy cost.
Practice Hess-law-style enthalpy estimates from first principles.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu