What Is Sublimation Definition Mechanism and Examples
Sublimation is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. Many real-life separation techniques, industrial processes, and even day-to-day phenomena are based on this concept.
What is Sublimation in Chemistry?
A sublimation process refers to the direct conversion of a substance from the solid state to the gaseous state, without passing through the liquid state. This concept appears in chapters related to states of matter, phase transitions, and physical and chemical changes, making it a foundational part of your chemistry syllabus.
Physical Principles of Sublimation
Sublimation occurs when the vapor pressure of a solid exceeds atmospheric pressure at a given temperature, allowing particles to escape directly into the air. The process usually requires heat, making it endothermic. Substances that can sublime include naphthalene, dry ice (solid CO₂), camphor, ammonium chloride, and iodine. These solids possess very weak intermolecular forces or special crystal structures, enabling this unique phase change.
Sublimation Process and Conditions
For sublimation to occur, specific conditions of temperature and pressure must be met. Everyday atmospheric pressure and a little heat are often enough for substances like camphor and mothballs. However, lower pressure or higher temperatures can enhance the process. The phenomenon is commonly explained using a phase diagram, which shows that sublimation happens below a substance’s triple point (where solid, liquid, and gas coexist).
| State | Phase Change | Example |
|---|---|---|
| Solid to Liquid | Melting | Ice to water |
| Solid to Gas | Sublimation | Dry ice, naphthalene |
| Liquid to Gas | Evaporation | Boiling water |
Examples of Sublimation
You will see sublimation both in laboratories and at home. Here are a few common examples for your understanding:
- Naphthalene balls kept in cupboards slowly disappear as they sublime into vapor, driving away insects.
- Dry ice or solid carbon dioxide, used for cooling and dramatic effects in parties or theatre, sublimates at room temperature to produce fog.
- Camphor, often used in worship, vanishes when left exposed to air due to sublimation.
- Iodine crystals, when heated, produce a violet vapor directly from the solid state.
- Ammonium chloride forms white fumes in labs by sublimation during heating.
| Substance | Sublimation Seen in |
|---|---|
| Naphthalene | Repellent balls in wardrobes |
| Dry Ice (CO₂) | Fog machines at events |
| Camphor | Religious offerings, air fresheners |
| Iodine | Lab experiments, antiseptics |
Applications of Sublimation
Sublimation is highly useful in real life and labs. Some major applications include:
- Purification: Used to separate volatile substances from non-volatile impurities, especially in separation techniques.
- Industrial Printing: The principle is used in dye sublimation printing on T-shirts, mugs, banners, and synthetic fabrics.
- Food Industry: Freeze-drying technique preserves food by sublimating frozen water directly into vapor, extending shelf-life.
- Medicines: Used in pharmaceutical processes for producing and storing sensitive vaccines and medicines.
- Air Fresheners: Sublimation ensures air freshener solids slowly vaporize into the room for a long-lasting fragrance.
Relation with Other Chemistry Concepts
Sublimation is closely related to evaporation, melting, and deposition (the reverse where gas turns directly to solid). It helps students bridge concepts between states of matter and energy changes, and is often connected to topics like endothermic reactions and phase diagrams.
Step-by-Step Sublimation Example
1. Place a mixture of common salt and ammonium chloride in a china dish.2. Heat gently under an inverted funnel so ammonium chloride sublimes and the vapors collect as solid on the cooler funnel walls, leaving salt behind.
3. The collected solid is pure ammonium chloride, illustrating separation by sublimation.
Lab or Experimental Tips
Always use proper ventilation when heating substances like iodine or ammonium chloride, as their vapors can be harmful. Vedantu educators recommend using an inverted funnel and cotton plug to contain fumes and to prevent loss of material during sublimation experiments.
Try This Yourself
- Name two household substances that undergo sublimation.
- Draw a simple diagram or flowchart showing the solid-to-gas transition in sublimation.
- Is sublimation a physical or chemical change? Explain why.
Final Wrap-Up
We explored sublimation—its scientific basis, examples, and importance in daily life and the laboratory. Sublimation is a unique physical change connecting many chemistry topics, from states of matter to industrial printing. Visit Vedantu for live sessions and detailed notes on related topics to strengthen your chemistry basics.
FAQs on Sublimation Process in Chemistry with Explanation
1. What is sublimation in chemistry?
Sublimation is a physical change in which a solid directly changes into a gas without passing through the liquid state. In this phase transition:
- The process occurs at temperatures below the substance’s boiling point.
- It is an endothermic process (absorbs heat).
- The chemical composition of the substance remains unchanged.
2. What are some common examples of sublimation?
Common examples of sublimation include solids that readily convert to vapour at room temperature or on heating. Examples include:
- Dry ice (CO2): CO2(s) → CO2(g)
- Iodine (I2): I2(s) → I2(g)
- Naphthalene (mothballs)
- Camphor
3. Is sublimation a physical or chemical change?
Sublimation is a physical change because only the state of matter changes while the chemical identity remains the same. During sublimation:
- No new substance is formed.
- The process is reversible by deposition.
- Intermolecular forces are overcome, but covalent bonds remain intact.
4. Why does sublimation occur?
Sublimation occurs because some solids have a high vapour pressure and weak intermolecular forces that allow particles to escape directly into the gas phase. It typically happens when:
- Intermolecular forces are relatively weak.
- The external pressure is low.
- The temperature is sufficient to overcome attractive forces.
5. What is the difference between sublimation and evaporation?
The main difference is that sublimation is solid → gas, while evaporation is liquid → gas. Key differences include:
- Sublimation: Occurs directly from solid to gas (e.g., CO2(s) → CO2(g)).
- Evaporation: Occurs from liquid surface to gas below boiling point.
- Sublimation skips the liquid state entirely.
6. What is deposition in relation to sublimation?
Deposition is the reverse of sublimation, where a gas changes directly into a solid without becoming liquid. In this process:
- Heat is released (exothermic).
- Gas particles lose energy and arrange into a solid structure.
7. How is sublimation used to separate mixtures?
Sublimation is used in separation of mixtures when one component sublimes and the other does not. The steps are:
- Heat the mixture gently.
- The sublimable solid converts directly to vapour.
- Cool the vapour on a cold surface to collect pure solid by deposition.
8. What conditions favor sublimation?
Sublimation is favored at low pressure and sufficient temperature to overcome intermolecular forces. Important conditions include:
- Low external pressure (below the triple point pressure).
- High vapour pressure of the solid.
- Weak intermolecular attractions.
9. What is the triple point in relation to sublimation?
The triple point is the temperature and pressure at which solid, liquid, and gas phases coexist in equilibrium. Below the triple point pressure:
- The liquid phase cannot exist.
- A solid changes directly to gas by sublimation.
10. Is sublimation an endothermic or exothermic process?
Sublimation is an endothermic process because it absorbs heat to overcome intermolecular forces in the solid. During sublimation:
- Energy is required to separate particles.
- The enthalpy change is called the enthalpy of sublimation (ΔHsub).
- ΔHsub equals enthalpy of fusion + enthalpy of vaporization.
