Sublimation Experiment for Schools, Teachers, and Students
Sublimation is the process in which a substance changes directly from a solid to a gas without passing through the liquid state. This occurs when the vapor pressure of the solid exceeds the atmospheric pressure at a specific temperature.
Theory:
- In sublimation, the particles of the solid absorb sufficient energy to overcome the forces of attraction and directly transition into the gaseous state.
- This process occurs at specific conditions of temperature and pressure where the liquid phase is skipped.
- Sublimation is an endothermic process as energy is absorbed to break the bonds between particles.
Examples of Sublimation:
- Dry Ice: Solid carbon dioxide (CO₂) sublimates directly into gas at -78.5°C under standard atmospheric pressure.
- Naphthalene Balls: These balls used in closets or drawers gradually sublimate into vapor, keeping insects away.
- Ammonium Chloride (NH₄Cl): On heating, solid ammonium chloride sublimes and reforms upon cooling.
- Camphor and Iodine: Camphor and iodine crystals sublimate at room temperature, producing a distinct odor.
Sublimation Curve:
The sublimation process can be represented on a phase diagram where the sublimation curve separates the solid and gaseous phases. At points on this curve, solid and gas coexist in equilibrium.
Latent Heat of Sublimation:
The latent heat of sublimation is the amount of heat required to convert a unit mass of a solid directly into a gas without any temperature change. The formula is:
Q = mLₛ
Where:
- Q: Heat energy absorbed (J)
- m: Mass of the solid (kg)
- Lₛ: Latent heat of sublimation (J/kg)
Applications of Sublimation:
- Freeze Drying: Used to remove moisture from food and pharmaceutical products by sublimating ice under reduced pressure.
- Purification of Substances: Sublimation is used to purify substances like ammonium chloride, camphor, and iodine.
- Insect Repellents: Naphthalene balls sublime to produce vapors that repel insects.
- Dry Ice in Cooling Systems: Dry ice is used for refrigeration and theatrical effects as it sublimates directly into gas.
Observations:
- Sublimation occurs without passing through the liquid state.
- Substances that undergo sublimation have low intermolecular forces.
- The latent heat of sublimation is higher than the latent heat of fusion.
- Sublimation occurs more readily under low-pressure conditions.
