 Okay, now let's try drawing a diagram for an endothermic reaction. If it's endothermic then energy is absorbed and our reactants at the beginning of the reaction have less energy than the products at the end. So in this case the enthalpy is going from a low value to a high value so the change is a positive one. Now again we need to show how the energy varies during the course of the reaction so we put in the activation energy to get things started. For an endothermic reaction activation energy has to be at least as big as the enthalpy change because if the reactants are going to be transformed into the products they need to get up to at least the enthalpy of those products. So we draw the activation energy up here and then there's a little decrease as the product molecules are formed and we end up at the product enthalpy level.