Bond Breaking and Making
Chemistry: AQA A Level, topic 1.4.2
Bond Breaking and Making
The basis of chemical reactions is a series of bond breaking and making.
Bond enthalpies
- During a reaction, some chemical bonds must be broken and made.
- The energy to break or make a bond is known as the bond enthalpy.
- Energy is needed to break a bond so it is an endothermic process.
- Energy is given off when a bond is made so it is an exothermic process.
- The enthalpy change of a reaction is a sum of the individual bond enthalpies being broken and made during the reaction.
The dominating term
- During a chemical reaction, we must determine whether the reaction requires more energy to break bonds or to make bonds.
- This will give an overall reaction enthalpy that is either positive or negative.
Endothermic vs exothermic
- Since bond breaking is endothermic and bond making is exothermic:
- More energy required to break bonds in a reaction will lead to an overall endothermic reaction.
- More energy released making bonds in a reaction will lead to an overall exothermic reaction.