3.1.4.4 - Bond enthalpies

Bond breaking

• Endothermic - requires energy to break bonds

• ΔH positive

• Stronger bonds take more energy to break

Bond making

• Exothermic - releases energy by breaking bonds

• ΔH negative

• Stronger bonds release more energy when they form

Bond enthalpy

The energy required to break bonds

Mean bond enthalpy

Average energy needed to break a certain type of bond, over a range of compounds

Always positive - breaking bonds = endothermic

Bond enthalpy variation

Energy needed to break a bond depends on its environment → same type of bond may require different amounts of energy to break

Enthalpy change of reaction formula

Enthalpy change of reaction = total energy absorbed - total energy released

Example bond enthalpy calculation