bond enthalpy

• Average bond enthalpy

  The energy required to break one mole a specified type of bond in a gaseous molecule
• bond enthalpies are always endothermic
• energy is always required to break bonds
• bond enthalpies always have positive values
• bond breaking is endothermic (ΔH is positive)
• bond making is exothermic (ΔH is negative)
• the difference between the energy required for bond breaking and the energy released by bond making determines whether an overall reaction is exothermic or endothermic
• the reaction is exothermic if the energy released when making bonds is greater than the energy required when breaking bonds
• the reaction is endothermic if the energy released when breaking bonds is greater than the energy released when making bonds
• ΔrH = total bond enthalpies in reactants - total bond enthalpies in products