9.3 Bond enthalpies

• Energy has to be put in to break bonds (endothermic)
• Energy is released when bonds are formed (exothermic)
• When more energy is released in forming new bonds than is needed to break bonds, overall energy change is exothermic
• When more energy is needed to break bonds than is released when new bonds are formed, overall energy change is endothermic
• Activation energy is the minimum amount of energy required for a reaction to take place
• Average bond enthalpy is the mean amount of energy required to break one mole of a particular covalent bond
• Average bond enthalpy is an average value obtained from many molecules containing the bond
• Average bond enthalpy is calculated by bond enthalpies in reactants - bond enthalpies in products