The difference between exothermic and endothermic reactions is found in their names: "endo" means to draw into itself, whereas "exo" means to emit. All chemical reactions either release or use energy, which can be in the form of heat or light. Endothermic reactions need energy that is supplied by their surroundings, whereas exothermic reactions give off energy. Exothermic reactions heat up their surroundings, while endothermic reactions cool them down.
Exothermic and endothermic reactions help to explain the first law of thermodynamics, which states that energy in the universe is conserved; it cannot be made or destroyed, only changed from one form to another. Examples of these two types of reactions are ice cubes melting, which is endothermic because it needs heat, and ice cubes being made from water, which is exothermic. Condensation formed from water vapor it exothermic, whereas water evaporating is endothermic. Cooking an egg and baking bread are endothermic, because they need heat from their surroundings, while a candle burning and iron rusting are exothermic.
Science 360 explains that exothermic reactions tend to be spontaneous while endothermic reactions tend not to be spontaneous. Enthalpy is the measure of the energy of a system. A drop in enthalpy means energy has been released by an exothermic reaction, whereas a positive change in enthalpy means an endothermic reaction has occurred.