AQA AS Chemistry

Revision Notes

1.6.1 Bond Energy

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

Chemical Energetics Bond Breaking and Forming, downloadable AS & A Level Chemistry revision notes

To break bonds energy is required from the surroundings and to make new bonds energy is released from the reaction to the surroundings

  • 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
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