Beginner Topic 134 of 1102 Bonding & Molecular Structure
Bond Energy
The energy needed to break one mole of a particular bond in the gas phase.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
In-depth explanation of Bond Energy
Bond energy, or bond dissociation enthalpy, is the average energy required to break one mole of a particular bond in gas-phase molecules. Breaking a bond always requires energy input, and forming one releases an equal amount. Values are averages taken over many different molecules, because the strength of a bond depends somewhat on its environment. Bond energies allow estimation of reaction enthalpies, using the approximation that the enthalpy change equals the energy of bonds broken minus the energy of bonds formed. Stronger bonds are generally shorter and less reactive.
Going deeper: Bond Energy
Key ideas: Use delta H of reaction approximately equal to sum of bonds broken minus sum of bonds formed. Example: for H2 + Cl2 giving 2 HCl, break 436 plus 243 and form 2 times 431, giving about -183 kJ. Bond energy values are for gas phase and average, so the result is an estimate within roughly 10 percent.
Common mistakes and connections: The sign error is the top mistake: bonds broken are endothermic and bonds formed are exothermic, so the subtraction is not reversed. Another slip is applying the method to liquids without including the enthalpy of vaporization. Connects to Hess's law, enthalpy of formation, bond order and thermodynamic stability.
Visualization of Bond Energy
Average bond enthalpies: multiple bonds are stronger than single ones, and N≡N at 945 kJ/mol is among the strongest, which makes N2 so unreactive. The interactive lesson shows this as a live animation or chart.
Worked example and use case
A typical C-H bond has an average energy of about 413 kJ/mol, while the O=O bond in O2 is about 498 kJ/mol.
Frequently asked questions about Bond Energy
What is Bond Energy?
The energy needed to break one mole of a particular bond in the gas phase.
Is Bond Energy a beginner, intermediate or advanced topic?
Bond Energy is a beginner topic in Bonding & Molecular Structure. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Bond Energy?
Study these earlier topics in Bonding & Molecular Structure first: Odd-Electron Molecules, Coordinate Bond, Bond Length.
What comes after Bond Energy?
The next topics in Bonding & Molecular Structure are Bond Order and Bond Polarity.
Can I practise Bond Energy with quizzes?
Yes. The interactive lesson includes a self-check question on Bond Energy, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Where Bond Energy fits in Bonding & Molecular Structure
Bond Energy is topic 19 of 104 in Bonding & Molecular Structure.