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

In exothermic reactions
This energy level diagram shows an exothermic reaction, we can tell this because the products are at a lower energy level than the reactants. The difference in height (ΔH) represents the energy given out in the reaction. ΔH is negative here because the reaction is giving out energy (as it is an exothermic reaction). The activation energy represents the energy needed to break the old bonds.


In endothermic reactions

This energy level diagram shown an endothermic reaction, we can tell this because the products are at a higher energy level than the reactants. The difference in height (ΔH) represents the energy taken. ΔH is positive because the reaction is taking in energy (because is an endothermic reaction).

Basis of notes source: CGP