No, dry ice is not boiling; it is sublimating.
While the process may superficially resemble boiling, a more accurate description is sublimation. Here's a breakdown:
Sublimation vs. Boiling
The key difference lies in the phase transition.
- Boiling: A liquid changes to a gas. For example, water (liquid) turns into steam (gas).
- Sublimation: A solid changes directly into a gas, bypassing the liquid phase. Dry ice (solid carbon dioxide) turns into carbon dioxide gas.
Why Dry Ice Sublimates
Dry ice, which is solid carbon dioxide (CO2), sublimates at a temperature of -78.5°C (-109.3°F) at standard atmospheric pressure. The bonds holding the CO2 molecules together in the solid state are relatively weak. Therefore, as the dry ice absorbs heat, the molecules gain enough energy to break free from the solid structure and transition directly into the gaseous state. Boiling involves a liquid phase, which dry ice skips under normal conditions.
Dry Ice in Water
When you place dry ice in water, you observe rapid sublimation, creating a fog-like effect. This is because the water provides heat that accelerates the sublimation process. The "bubbling" appearance is actually the carbon dioxide gas escaping from the solid dry ice.
Analogy
Imagine ice cubes disappearing in your freezer. They are sublimating, though much more slowly. Dry ice just does this much more rapidly and visibly because of its lower sublimation temperature.
