energy change of reactions

• energy is supplied to break bonds in the reactants
• energy is released to make bonds in the products
• describe bond energies in an exothermic reaction

  the energy released from making new bonds is greater than the energy needed to break existing bonds
• describe bond energies in an endothermic reaction

  the energy needed to break existing bonds is greater than the energy released from forming new bonds
• bond energy equation

  energy of reaction= sum of bonds broken - sum of bonds made