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Sublimation: Definition, Principle, Demonstration, Examples and Applications


You must have seen different reality shows or live concerts where smoke is used to create a dramatic effect on the stage, or at least a cloud scene in a cinema. This is called "theatrical smoke and fog." This is formed using dry ice, which is a solid form of carbon dioxide. 

The smoke is created by a process called sublimation in fog machines in which a solid form of carbon dioxide is directly converted into its vapour form at a particular pressure and temperature conditions.


In our daily lives, we see substances in a multitude of states, which are referred to as states of matter. We are familiar with substances in either solids, liquids, or gaseous states. Each of them represents a different stage of the subject depending on the physical conditions of temperature and pressure. We all know that substances change phases, for example, from solid to liquid to gas on increasing temperature and decreasing pressure. In rare cases, a solid can enter the gas phase directly without passing through the liquid phase. The name for such a process is sublimation. The material and examples that follow will assist you in comprehending the idea.

Table of content:

Sublimation


Sublimation is the process of converting a substance from a solid to a vapour state directly without passing through the liquid phase on heating and vice versa on cooling.


The process of sublimation is used for those substances which sublime on heating from a non-volatile substance. Organic compounds that have covalent bonds are easily sublime compared to ionic compounds.

De-sublimation, or deposition, is the inverse of this process, in which the gas transitions directly towards the solid phase. This is an endothermic phase transition that occurs when the heat and pressure of a substance fall below their triple point. As a result, energy is given away in the reversal process.

Sublime refers to a solid substance that transforms into a gas. Sublimate is the solid that results from the cooling of vapour. It is critical to remember that the term "sublimation" only applies when a completely physical change of state occurs.

Principle of Sublimation


Sublimation is based on the principle that solids have a weak intermolecular force, resulting in a higher vapour pressure, which changes them to a vapour state directly.

Demonstration

1. Take an impure benzoic acid or naphthalene ball in a china dish.
2. Place an inverted funnel on a china dish after covering it with filter paper.
3. Close the funnel stem with cotton.
4. When the dish is heated in a sand bath, the vapours of the benzoic acid rise up.
5. The vapours of benzoic acid condense on the wall of the funnel.
6. Non-volatile impurities remain in the china dish.
7. Remove the funnel to collect the deposited benzoic acid.


Examples of sublimation

 

  • Sublimation is demonstrated by dry ice, which is a frozen form of carbon dioxide. When dry ice is exposed to the air, it transforms from a solid to a gaseous state.
  • Iodine treatment: The iodine crystals have been converted into the typical purple gas under laboratory heating.
  • Corrosive gas sublimation: Some metallic vapours, like mercuric chloride, will inversely sublimate, which is a common degrading step in alchemical activities. 
  • Frost formation: Water vapour undergoes reverse sublimation at very cold temperatures, forming ice crystals on surfaces, which is known as "frost."
  • The continuous snow on the mountain peaks persists in a semi-solid state, which allows it to revert to vapour without going through its liquid condition.

Application of sublimation

 

  • In the forensic sciences, sublimation can be helpful. Iodine sublimation can be employed to expose forensic evidence on paper.
  • Sublimation is a chemist's purification method for purifying volatile compounds. It's very useful for organic compounds.
  • Inkjet printers have been replaced by dye-sublimation printers. Because the prints dry faster, the printouts are ready to use as soon as they come out of the printer.
  • Dye sublimation is a printing technique used in the textile industry to print synthetic materials like polyester.
  • T-shirts, flags, and banners can all be made using this process.
  • For a reduced cost, dye sublimation is used to print a variety of objects such as pens, coffee mugs, and bags.
  • This method is used by space agencies like NASA and ISRO to supply high-quality meals to astronauts in orbit. When a food product must be stored for an extended period of time, this method is used.
  • In the frozen food industry, freeze-drying is a popular application of sublimation. Frozen water in the substance sublimates from the solid to the gas phase when the surrounding pressure is reduced.
  • It is safe and environmentally friendly, and no trash is produced during the process.

Practice Problems
 

Q 1.  Which substance will separate first from a mixture of sand, salt, and benzoic acid? 

a. Sand
b. Benzoic acid
c. Salt
d. Sand and benzoic acid

Solution: B)

Benzoic acid will be separated first by sublimation, and the other two be separated by filtration after dissolving in water.

Q 2. During sublimation, what happens to the atoms? 

a. They accelerate by gaining energy and spread out more
b. They accelerate by gaining energy and coming close to each other
c. They slow down by losing energy and moving closer together
d. They slow down by losing energy and spreading out more

Solution: A)

Sublimation process is an endothermic process where atoms in solid-state absorb energy and get converted to a gaseous state. 

Q 3. Sublimation process used to purify compounds present in which state? 

a. Plasma
b. Liquid
c. Solid
d. Vapour

Solution: C)

Solid substances which are volatile in nature are separated from non-volatile substances.

Q 4. What are the atmospheric pressure conditions at high altitudes where sublimation of ice takes place  ? 

a. High
b. Low
c. Liquid
d. 1 atm

Solution: B)

Sublimation of ice takes place at high altitudes where atmospheric pressure is low.

Q 5. What happens to the water molecules when wet clothes are dried on sunny days? 

a. Gains heat energy and evaporates
b. Lose heat energy and evaporates
c. Gains heat energy and condenses
d. Lose heat energy and condenses

Solution: A)

Water molecules gain energy and evaporate.

Frequently asked questions

Q 1. What is the process for conversion of gaseous phase to solid phase?

Answer: The process for conversion of the gaseous phase to the solid phase is known as deposition by keeping the pressure and temperature below the triple point. 

Q 2. How would you separate a sand and camphor mixture? 

Answer: By sublimation sand and camphor mixture is separated as camphor is a volatile substance that sublimes to vapours and sand remains.

Q 3. Give some examples of sublimating substances?

Answer: Benzoic acid, ammonium chloride, and camphor are volatile in nature, so these are the examples of sublimating substances. 

Q 4. Is heat required for sublimation?

Answer: Yes, heat is required for sublimation. The amount of energy that must be delivered to a solid mole under constant pressure to turn it directly into a gas is known as the sublimation enthalpy (without going through the liquid phase).

Q 5. Why are temperature and pressure conditions required for sublimation?

Answer: In the sublimation process, the phase transition is taking place which depends on the condition of temperature and pressure. When pressure and temperature conditions are below triple point, a solid substance directly sublimes into vapour.

Related Topics 

Filtration and Decantation Distillation
Crystallization Chromatography
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