By Allison Boley | Updated Aug 30, 2022

What Is Sublimation?

Sublimation is the direct transition of a substance from the solid phase to the gas phase, bypassing the liquid state entirely. The process occurs when the temperature and pressure of a material place it in a region of the phase diagram where the solid and gas phases are in equilibrium.

States of Matter

All familiar matter exists in one of three principal phases: solid, liquid, or gas. These phases are distinct states of the same chemical substance. For instance, water exists as ice (solid), liquid water, or steam (gas), all with the same chemical formula, H₂O.

Phase Transitions

The most common transitions are melting (solid to liquid) and boiling (liquid to gas). Sublimation, by contrast, moves directly from solid to gas. The reverse process—gas to solid—is called deposition.

Phase Diagrams Explained

A phase diagram maps temperature (x‑axis) against pressure (y‑axis) to illustrate where each phase exists. To induce sublimation, the system must be below the solid–liquid boundary and below the liquid–gas boundary, typically at low pressure. The single solid–gas line on the diagram marks the conditions for direct conversion.

Latent Heat of Sublimation

When heat is added to a solid, its temperature rises until it reaches the solid–gas transition line. At that point, further energy input does not increase temperature but instead supplies the latent heat required to break the bonds that hold the solid together. This energy is the latent heat of sublimation. When the gas condenses back to solid, the same amount of heat is released.

Real‑World Examples

• Dry ice: Solid carbon dioxide (CO₂) that sublimes at −78.5 °C, producing a cold, invisible gas without a liquid phase.
• Iodine: A violet solid that can sublimate at room temperature, often seen as a faint purple vapor.
• Naphthalene: Used in mothballs, this organic compound readily sublimates, releasing a characteristic odor.
• Freeze‑drying: Foods are frozen and then subjected to a vacuum so that ice sublimates directly to water vapor, preserving texture and flavor.

These examples illustrate how sublimation is not only a fundamental physical phenomenon but also a practical tool in science and industry.