Solid carbon dioxide (dry ice) converts directly to gas at room temperature. How is this process classified?

Core Concept

Sublimation takes molecules from a rigid solid straight to gas, which requires breaking away from the intermolecular attractions of the solid. That energy comes from the surroundings, which is why dry ice cools everything near it. Absorbing energy makes ΔH positive, the definition of an endothermic process. Freezing, condensing, and combusting all run the other way and release energy.