Endothermic vs. Exothermic: Reactions are classified into two types, exothermic and endothermic reactions, depending upon their giving or taking of energy. The main difference between endothermic and exothermic reactions is that endothermic reactions take place when the system takes up energy, while in exothermic reactions, the system gives up energy in the form of heat or light. Moreover, in an endothermic reaction, energy is absorbed, while in an exothermic, energy is released in the surroundings.