Sublimation is an endothermic process. This means that when a substance transitions from a solid to a gas, it absorbs heat from its surroundings. A common example of sublimation is dry ice, which is solid carbon dioxide. When dry ice is exposed to air, it doesn’t melt into a liquid but instead converts directly into carbon dioxide gas. This absorption of heat is why the surrounding area feels colder when dry ice is present.
During sublimation, the molecules in the solid phase gain enough energy to break free from their fixed positions in the solid structure and move into the gas phase. This requires energy input, typically in the form of heat. Thus, because heat is absorbed in the process, sublimation is classified as an endothermic reaction.