- Evaporation
- Sublimation
- Condensation
- Fusion
Sublimation is the phase transition in which a substance changes directly from solid to gas without passing through the intermediate liquid state. This endothermic process occurs when molecules gain sufficient energy to overcome intermolecular forces and escape the solid lattice directly into the vapor phase. Common examples include dry ice (solid carbon dioxide) at atmospheric pressure, which sublimes at -78.5°C, producing visible fog without melting. Mothballs (naphthalene or paradichlorobenzene) also sublime gradually, releasing vapor that repels insects. Iodine crystals heated gently produce purple vapor without melting, demonstrating sublimation visibly. The reverse process, gas directly to solid, is called deposition (e.g., frost formation). Sublimation requires specific temperature-pressure conditions below the triple point where all three phases coexist. Applications include freeze-drying (lyophilization) for food preservation and pharmaceuticals, where frozen water sublimes under vacuum, leaving dehydrated product. In forensic science, sublimation is used to develop fingerprints. Understanding sublimation is crucial in materials science, atmospheric physics (snowpack changes), and various industrial processes.
