Bond Enthalpy – A Level Chemistry Edexcel Revision

Bond enthalpy refers to the energy involved in the formation or breakage of chemical bonds. It is expressed in kilojoules per mole (kJ/mol).
Bond breaking is an endothermic process, which means it requires energy input. This is because the atoms involved need to overcome forces of attraction holding them together in order to separate.
On the other hand, bond formation is an exothermic process; it involves energy release. This is due to new forces of attraction being established between atoms, bringing them closer together which is a more stable state.
The bond enthalpy is usually quoted for the gaseous state, as the enthalpy change in a chemical reaction is only dependent on the initial and final states, not the reaction path.
Catalysts do not change the bond enthalpy of reactants or products, but they lower the activation energy of the reaction, which is the energy required to start a chemical reaction.
Bond enthalpy values can differ depending on whether we are considering the energy required for breaking the bond in the gaseous phase, forming it in the gaseous phase or in different molecules.
When comparing bond enthalpy values, triple bonds are stronger than double bonds, which are in turn stronger than single bonds.
In addition to being useful for predicting whether a chemical reaction is feasible or not, bond enthalpies can also be used in calculations involving Hess’s Law to determine overall energy changes in multi-stage chemical reactions.
When approaching calculations using bond enthalpies, it is important to note that the value represents the enthalpy change for breaking one mole of bonds in gaseous molecules.
It is important to understand and correctly apply the sign conventions for bond enthalpy: negative values signify energy being released (exothermic reactions) while positive values represent energy being absorbed (endothermic reactions).
Understanding bond enthalpy is essential to many areas of chemistry, including analysing reaction mechanisms, investigating the behaviour of gases, and the stability and reactivity of molecules.