Which phase change occurs when a solid turns directly into a gas?

• A. Sublimation
• B. Deposition
• C. Vaporization
• D. Condensation

Answer: (A)

The process in which a solid transitions directly into a gas is known as sublimation. This physical change occurs without the substance passing through the liquid phase. A common example of sublimation is dry ice (solid carbon dioxide) turning into carbon dioxide gas at room temperature.

Sublimation is significant because it demonstrates the ability of certain substances to convert directly from solid to gas under specific conditions of temperature and pressure, bypassing liquid formation entirely. This property has practical applications in various fields, such as freeze-drying in food preservation and the manufacturing of certain chemicals and materials.

The other processes listed involve different phase changes: vaporization refers to the transition from liquid to gas, condensation is the process of gas turning into liquid, and deposition is when a gas transforms directly into a solid. Understanding these differences helps clarify the unique nature of sublimation among the various phase changes.