Introduction
You would have noticed a change in the state of matter when ice changes to water or when water changes to vapour. These are the physical changes in the states of matter. These changes occur when the substance absorbs or loses energy. These changes include: freezing, melting, condensation, evaporation, sublimation, and deposition.
The changes are divided into the following categories:
- The conversion between Liquids to Solids
- The conversion between Solids to Gases
- The conversion between Liquids to Gases; and vice versa.
Freezing and Melting belong to the first category, i.e. Change from liquids to solids and vice versa. When a matter changes from a solid to a liquid state, it is known as Melting. When a matter changes from liquid to solid form, it is called Freezing.
Sublimation and Deposition belong to the second category, i.e. Change from solid to liquid and vice versa. When a substance changes its phase, temperature and pressure are the factors that cause this transition. When a solid matter's temperature rises, it gets converted into a liquid state. Although, there are some substances which get converted directly to the gaseous state.
Evaporation and Condensation are from the third category, i.e. Change from liquid to gaseous form and vice versa. In Evaporation, liquid converts into its gaseous form on heating. On the other hand, in condensation, gas gets converted into a liquid state on cooling.
These are known as Physical Changes. Physical changes involve changes in the shape, size, colour, and state of the substance being transformed. The composition does not get affected, and therefore, most changes are reversible. The substance can come back to its original state in physical change. These changes include the following factors:-
- Nature of the matter
- Surface Area
- Humidity
- Temperature
- Pressure
Sublimation vs Deposition
'Sublimation and Deposition’ belonging to the transformation in the state of matter category, are different from each other in various aspects. Even though the conversion happens between the solid and liquid states, they are quite the contrary.
Sublimation is a phase where the solid changes into a gaseous form, without going through the liquid state. Deposition, on the contrary, is a phase when the gas gets converted into a solid form, without experiencing the liquid state. These two are examples of phase changes. These phenomena can only occur at a particular temperature and pressure. Just like how 'freezing and melting', 'evaporation and condensation' are different from one another, in the same way, 'sublimation and deposition' are distinguishable in varied aspects and parameters.
Difference Between Sublimation and Deposition in Tabular Form
| Parameters of Comparison | Sublimation | Deposition |
| Definition | Sublimation is the transition in which the substance transforms directly from solid to gas. | Deposition is the transition phase in which a substance changes from gaseous to solid state directly. |
| Energy Consumption | Sublimation consumes a lot of energy. | Deposition releases a lot of energy in its process. |
| Process | It is an endothermic person in which the reactants absorb heat. | It is an exothermic process in which the reactants release heat and energy. |
| Heat | Heat gets absorbed in the process of Sublimation. | Heat is released in the Deposition process. |
| Purpose | Sublimation is used in breaking substances to obtain their purified state. | Deposition is used in making substances for storing them in solid form. |
| Molecular activity | The molecules go directly from solid to gaseous form. | The molecules settle out of the gaseous state into the solid form. |
| Example | Dry-ice or carbon dioxide, air fresheners, Naphthalene balls, and some medications that sublime if heated. | Frost formation, snow, soot molecules, etc. |
What is Sublimation?
Sublimation is a physical change of matter when the solid modifies directly into the gaseous state, without getting converted into liquid.
It only applies to the physical conversion of matter and not a chemical change. The factors on which the temperature and pressures under which sublimation occurs depend are:- the chemical and physical properties of the substance. The phenomenon of sublimation is the outcome of the vapour pressure and temperature relationship.
Sublimation is an endothermic phenomenon that transpires below a substance's 'triple point'.
Example of Sublimation
- Solid Carbon Dioxide/Dry-Ice is the most famous example of sublimation. Solid carbon dioxide sublimates into carbon dioxide gas at room temperature and pressure. The room temperature is accepted as 293 Kelvin, along with the pressure of 1.01 Bar.
- Diamond, iodine, ammonium chloride, and graphite also sublime completely at air pressure.
- When Ammonium Chloride is heated, it goes directly into its vapour form. When these vapours are cooled, it gets back to their original Ammonium chloride state.
- Arsenic also sublimes at 615 degrees.
- Iodine crystals when heated at a temperature of 100 degrees display a formation of purple-coloured gas.
- Sulphur sublimates into toxic gas at a temperature between 25 to 50 degrees.
- The Dye Sublimation process also helps in criminal investigation by aiding forensic experts in their forensic investigation.
Process of Sublimation
Before understanding the process of sublimation, let's have a look at some of the key terms related to it.
Endothermic Reaction - The chemical reactions in which the reactants absorb heat energy from the surroundings to form products. This reaction reduces the temperature of the enclosing area, thus creating a cooling effect.
The energy corresponding to the transformation between solids and liquids is known as Latent Heat of Sublimation.
The Enthalpy of Sublimation - Enthalpy of Sublimation is the heat or energy required to convert the state from solid to gaseous. It is unique to each substance and commonly expressed in KJ/mol or KJ/kg.
For the Sublimation process to be successful, some criteria need to be acknowledged:-
- The sample substance should be accommodated at a sufficient temperature to maintain high vapour pressure.
- If it goes below that temperature, the substance can get decomposed.
- A surface must be available for the vapoured substance to condense or solidify.
Sublimation and Evaporation
Though they both get transformed into gaseous states, they are still different from each other. In sublimation, the solid gets converted into a gaseous form. On the other hand, in evaporation, the liquid state is converted into a gaseous state.
Application of Sublimation
- It is a very effective method for separation and purification. Sublimation can be applied as a purification method when a solid substance gets contaminated with non-volatile adulterations.
- 'Air freshener' is also an appropriate example of sublimation in our day-to-day life. You can see the transition from a solid to a gaseous phase when air fresheners get heated in a hot water bathtub.
- Mothballs, popularly known as Naphthalene Balls, help to keep insects away. They are also a case of sublimation.
- The frozen food industry is also a widely-spread example of sublimation. When the surrounding pressure is allowed to get diminished, the iced water in the substance will sublimate from the solid form to the gaseous.
- Many pharmaceutical companies also use this technique for storing products and manufacturing raw materials.
- The Inkjet printers are slowly getting replaced by Dye sublimation printers because the printed material gets dried quickly, and additionally, these are easy to maintain.
- Many decorative works get implemented using the sublimation method.
- Sublimation allows the manufacturing of full-colour plaques, signs, name badges, etc., which aid in the domain of awards and recognitions.
- Coffee mugs, pens, bags, and t-shirts can be etched using the dye sublimation mechanism.
What is Deposition?
The deposition process is the direct conversion of the gaseous state into a solid state without changing into liquid. This process is the opposite of sublimation therefore, it is sometimes also known as 'de-sublimation'. Deposition occurs when the temperature is frigid or below the freezing point. The deposition is an exothermic process. For the deposition process to occur the chemical system needs to release energy into the surroundings.
First, let's understand some terms that are mentioned in the above paragraph.
Exothermic Process or Exothermic reaction- An Exothermic reaction is one in which energy gets discharged, in the guise of light or heat, in the surroundings. In simple words, in an exothermic reaction, heat is transferred into the surroundings instead of absorbing heat from the surrounding area.
Freezing Point- The freezing point is the temperature of a substance at which a liquid becomes solid. It is considered to be 32 degrees Fahrenheit or zero degrees Celsius. Deposition occurs when the temperature is even below the freezing point. For instance, the freezing point of carbon dioxide is -78.5 degrees Celsius or -109.3 degrees Fahrenheit.
Examples of Deposition
- An example of deposition is when warm moist air comes in contact with a cold surface, ice crystals get deposited. These crystals are known as Frost. For instance - If you look at leaves or blades of grass during winter, you will notice frost on them.
- The deposition also occurs high above the ground when the water vapour into ice crystals. In the atmosphere, ice crystals get deposited on dust particles.
- The soot that gets deposited on chimneys is also an example of deposition. Soot molecules arise from the fire in the gaseous form.
- For achieving anti-reflective effects, magnesium fluoride is deposed on optical lenses.
- Titanium Nitride is utilised for preventing rusting on tool wear.
- Chemical Deposition helps manufacture reflective coating in mirrors.
Application of Deposition
- The most famous example of deposition is Frost. So, what exactly is Frost? Frost is the deposition of ice crystals from humid air onto a solid surface. Rime will get formed when the deposition site is at a lesser temperature than the freezing point of water and, the surrounding air is humid or damp. Snow is also a specimen of deposition. The water vapour in the clouds changes directly to ice, skipping the liquid phase of water. It can only occur at freezing temperatures. In the clouds, water vapour is at frigid temperatures and loses its thermal energy before coming down. As it transcends onto the earth's surface, it gets altered into snow.
- Various chemical vapours can depose to form films on the surface. For instance, Bug bombs that are used to get rid of parasites release a gaseous pesticide in the house, the pesticide comes in contact with the household surface and deposes into a sticky film and helps trap parasites and insects.
- This process is also used to form dry ice from carbon dioxide. After placing carbon dioxide gas in a chamber, the temperature and pressure are adjusted for the process of Deposition.
- The deposition process is also responsible for lung obstruction, which results from inhaling pollutants present in the air. It can be toxic as well.
Main Differences Between Sublimation and Deposition In Points
- In sublimation, solid changes directly into the gaseous state without changing into liquid. In Deposition, gas changes into a solid without passing the liquid form.
- Deposition releases a lot of energy at a high rate. Sublimation, on the contrary, requires a lot of energy as the heat is absorbed from the surroundings.
- Sublimation is an endothermic process whereas Deposition is an exothermic process. In the Endothermic process, heat is absorbed and in the Exothermic, a high amount of heat is released.
- Sublimation is required to break down the chemical components of a substance to obtain its purified form. The deposition method is necessary for making a solid substance from its vapour form.
- In Sublimation, molecules travel from solid to gas. In Deposition, molecules transfer from gaseous to solid form. They both are in complete contrast with each other.
Conclusion
Sublimation and Deposition are physical changes but different from each other in the process of conversion of the state of matter. The main difference between the two is that - in Sublimation, the conversion takes place from solid to gaseous state whereas, in Deposition, the substance gets converted from gaseous form to solid form. The similarity between Sublimation and Deposition is that they both involve a solid and gaseous state of matter.
There are many terms in the subject of chemistry that some may find confusing, especially in the change of state of matter differentiating between two physical changes is an important topic to cover and clear whatever the reason for the confusion is.
References
- https://energyeducation.ca/encyclopedia/Sublimation_and_deposition
- https://en.wikipedia.org/wiki/Deposition_(phase_transition)