Short Answer

Sublimation is the process in which a solid changes directly into a gas without passing through the liquid state. This happens when the solid absorbs enough heat for its particles to break free and escape into the air as gas. Common substances that undergo sublimation include camphor, dry ice (solid carbon dioxide), and naphthalene balls.

Sublimation is a physical and reversible change because the gas formed can change back into a solid on cooling. This special process shows how particle movement and heat energy affect the state of matter.

Detailed Explanation :

Sublimation

Sublimation is a special type of physical change in which a solid changes directly into a gas without becoming a liquid first. Unlike melting, where a solid turns into a liquid, sublimation skips the liquid stage. This process happens in substances whose particles have enough energy to break away from the solid structure and escape directly into the gaseous state.

Sublimation usually occurs when a solid absorbs heat from the surroundings. As the temperature rises, the particles in the solid vibrate faster. If the solid has weak intermolecular forces, the particles can separate completely and turn into gas. This process is reversible because the gas produced can cool down and turn back into a solid without forming a liquid.

Sublimation is commonly seen in everyday life and has many practical uses. It also helps us understand how different materials behave under different temperatures.

How Sublimation Happens

1. Absorption of Heat

Sublimation begins when a solid absorbs heat energy. This heat increases the vibration of the particles.

• Particles move faster.
• Kinetic energy increases.
• Attraction between particles weakens.

In some solids, this increase in energy is enough for the particles to escape directly into the air as gas.

2. Weak Intermolecular Forces

Only solids with weak forces of attraction between their particles undergo sublimation. Because the attraction is weak:

• The structure breaks easily.
• Particles do not stay tightly packed.
• They leave the solid surface and become gas.

Examples include camphor and naphthalene, which slowly disappear when kept in open air.

3. No Liquid Stage

A unique feature of sublimation is that there is no liquid stage. The change happens directly:

Solid → Gas

There is no formation of water-like liquid in between. This is what makes sublimation different from melting, evaporation, and boiling.

4. Cooling and Reverse Sublimation (Deposition)

The gas formed during sublimation can cool down and turn back into a solid. This reverse process is called deposition.

Example:

• Dry ice (solid CO₂) forms frost-like solid CO₂ under cold conditions.

This shows that sublimation is a reversible physical change.

Examples of Sublimation

1. Camphor

Camphor evaporates slowly at room temperature. It gives off a strong smell because it turns directly into vapor.

2. Naphthalene Balls

Used in cupboards to protect clothes from insects, naphthalene balls slowly become smaller because they sublimate into gas.

3. Dry Ice

Dry ice is the solid form of carbon dioxide. It does not melt into liquid. Instead, it changes directly into carbon dioxide gas.

4. Iodine Crystals

Iodine, when heated, forms purple-colored vapor without turning into liquid.

5. Ammonium Chloride

When heated, it breaks down and turns into gas directly.

These examples show that sublimation is a natural and common phenomenon.

Conditions That Support Sublimation

Sublimation occurs under certain conditions:

• Low pressure: Higher chances of solid turning into gas.
• High temperature: Particles get enough energy to escape.
• Weak intermolecular forces: Solids that do not hold particles tightly are more likely to sublimate.

Uses of Sublimation

Sublimation has many practical applications:

1. Purification of Substances

Some solids can be purified through sublimation because their impurities do not sublimate.

2. Air Fresheners

Solid air fresheners slowly sublimate and release fragrance into the air.

3. Food Preservation

Dry ice is used to keep food cold because it sublimates without leaving water behind.

4. Printing Technology

Sublimation printing is used to transfer designs onto fabrics and materials.

5. Making Medicines

Some chemicals used in medicines are prepared using controlled sublimation.

Difference Between Sublimation and Other Changes

• Melting: Solid → Liquid
• Boiling/Evaporation: Liquid → Gas
• Condensation: Gas → Liquid
• Freezing: Liquid → Solid
• Sublimation: Solid → Gas

This shows that sublimation is unique because it skips the liquid phase entirely.

Conclusion

Sublimation is the process in which a solid changes directly into a gas when heat is absorbed, without passing through the liquid state. It occurs in substances with weak intermolecular forces and is a reversible physical change. Sublimation is seen in many everyday materials such as camphor, dry ice, and naphthalene balls. It has important uses in purification, cooling, printing, and household applications, making it a significant concept in the study of matter.