Sublimation is the phase transition where a solid changes directly into a gas, bypassing the liquid phase entirely.
How it works:
- At certain pressures and temperatures (usually low pressure or heat under specific conditions), some solids gain enough energy for their molecules to break free directly into the vapor phase.
- This occurs when the substance’s vapor pressure exceeds the ambient pressure at a temperature below its melting point.
Common examples:
- Dry ice (solid CO₂) sublimates at room temperature, turning directly into carbon dioxide gas.
- Snow and ice can sublimate in cold, dry air, even if they don’t melt.
- Iodine crystals and naphthalene (in mothballs) also show sublimation behavior.
Sublimation is used in freeze-drying, purification techniques, and occurs naturally in environments like cold deserts or outer space.