4.13 represent exothermic and endothermic reactions on a simple energy level diagram

4.13 •exothermic reactions have a -ve enthalpy change 

                   •the products are at a lower energy than the reactants

                   •the initial rise in the line represents the energy needed to break the old bonds

                             •this is the activation energy  

                                      *google for images*

      

        •endothermic reactions have a +ve enthalpy change

                  •the products are at a higher energy than the reactants

                  •the difference in height represents the energy taken in during the reaction