What is the process called when a solid changes directly into a gas?

• A. Evaporation
• B. Condensation
• C. Sublimation
• D. Melting

Answer: (C)

Sublimation is the process by which a solid changes directly into a gas. This happens when the solid’s molecules gain enough energy to overcome the intermolecular forces holding them in the solid, so it skips the liquid phase entirely. A classic example is dry ice (solid carbon dioxide) at room temperature and atmospheric pressure, which turns directly into carbon dioxide gas without melting. Other substances, like solid iodine or naphthalene, can also sublime under the right conditions.

For comparison, evaporation is liquid turning into a gas, condensation is gas turning into a liquid, and melting is solid turning into a liquid. In hazmat contexts, sublimation can release significant amounts of gas quickly, so awareness of pressure and temperature conditions is important for hazard assessment.