Sublimation is a physical change in which a substance directly changes from the solid state to the gaseous state without passing through the liquid state. This process takes place when the particles of a solid absorb heat energy and gain enough energy to overcome the forces of attraction between them.
As a result, the particles escape from the solid and move freely as a gas. On cooling, the gas can directly change back into a solid without becoming a liquid. This reverse process is called deposition.
Examples:
- Camphor
- Naphthalene balls
- Ammonium chloride
Characteristics of Sublimation
Sublimation has some important features that explain this process:
- It is a physical change, so no new substance is formed.
- The substance changes directly from solid to gas without becoming liquid.
- It occurs in substances with weak intermolecular forces of attraction.
- The process is reversible (gas can change back into solid by cooling).
- It requires absorption of heat energy (endothermic process).
Process of Sublimation
The process of sublimation involves the direct change of a substance from solid to gas and back to solid.
- When a sublimable solid is heated, its particles absorb heat energy and gain enough energy to overcome the forces of attraction between them.
- As a result, the solid changes directly into vapours (gas) without becoming liquid.
- These vapours, when brought in contact with a cold surface, lose heat and directly change back into solid form.
- This reverse process is called deposition.
Example: Ammonium chloride sublimes on heating and forms solid again on cooling.
Applications of Sublimation
Sublimation is used in many areas of daily life, laboratories, and industries:
1. Separation of Substances: Sublimation is used to separate a sublimable solid from a non-sublimable substance.
2. Purification of Solids: It is used to purify substances that can sublime. Impurities remain behind, while the pure substance vaporizes and then solidifies again.
3. Use in Moth Repellents and Fragrances: Substances like naphthalene balls and camphor sublime slowly. It protect clothes from insects, provide fragrance.
4. Freeze-Drying (Preservation): Sublimation is used in freeze-drying to preserve Food items and Medicines. Water is removed directly as vapour, keeping the material safe.
5. Printing Technology: Used in dye-sublimation printing for printing on clothes, mugs, etc. Gives high-quality and long-lasting prints.
6. Drying of Materials: Used in laboratories to dry heat-sensitive substances without turning them into liquid.
7. Space and Scientific Uses: In very low-pressure conditions (like space), substances can sublime easily, which is important in scientific studies.
Examples of Sublimation
Some examples where sublimation is used are,
- Dry Ice (Solid Carbon Dioxide): The example of sublimation widely spread in nowadays is dry ice. It undergoes sublimation at atmospheric pressure into a gaseous state and produces a fog-like effect.
- Iodine Crystals: Iodine in solid form sublimes on heating. Iodine crystals do not turn to liquid when they become exposed to the air, but rather convert directly into purple vapors.
- Naphthalene: Another substance which sublimates is naphthalene commonly found in moth balls. Naphthalene molecules have a tendency of turning into gas over time and gradually mothballs get smaller.
- Camphor: This solid form of camphor that is common in some medical products or moth repellents volatilizes at room temperature producing its odor molecules.
- Ammonium Chloride: Solid ammonium chloride is a common laboratory substance and it sublimes on heating, giving off white vapors. This feature enables its use for many chemical procedures..