Bond Energy
- During a reaction, enthalpy changes take place because bonds are being broken and formed
- Energy (in the form of heat) is needed to overcome attractive forces between atoms
- Bond breaking is therefore endothermic
- Energy is released from the reaction to the surroundings (in the form of heat) when new bonds are formed
- Bond forming is therefore exothermic
To break bonds energy is required from the surroundings and to make new bonds energy is released from the reaction to the surroundings
- The sum of the energy in and energy out determines whether the reaction is overall exothermic or endothermic
- If more energy is required to break bonds than energy is released when new bonds are formed, the reaction is endothermic
- If more energy is released when new bonds are formed than energy is required to break bonds, the reaction is exothermic
- In reality, only some bonds in the reactants are broken and then new ones are formed
