Sublimation (phase transition): Difference between revisions

Revision as of 07:19, 1 December 2023

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<!-- READ BEFORE EDIT, sublimation refers to ALL THREE CASES:

1. the transition below triple point and below boiling point
(similar to evaporation)
(bottom left of solid in phase diagram)

2. the transition below triple point and at boiling point
(similar to boiling)

3. the transition above triple point and below melting point
(also similar to evaporation)
(top left of solid in phase diagram)
(yes, solid sublimes above triple point)

- the definition is simply the transition of a substance directly from the solid to the gas state, without passing through the liquid state -->

[[File:Nickelocen an einem Kühlfinger.jpg|thumb|right|Dark green [[crystals]] of [[nickelocene]], sublimed and freshly deposited on a [[cold finger]]]]

'''Sublimation''' is the [[Phase transition|transition of a substance]] directly from the [[solid]] to the [[gas]] state,<ref>{{cite Merriam-Webster|Sublimate}}</ref> without passing through the [[liquid]] state.<ref>{{cite book |last1=Whitten |first1=Kenneth W. |last2=Gailey |first2=Kenneth D. |last3=Davis |first3=Raymond E. |title=General chemistry |url=https://archive.org/details/generalchemistry00whit_0 |url-access=registration |date=1992 |publisher=Saunders College Publishing |isbn=0-03-072373-6 |page=[https://archive.org/details/generalchemistry00whit_0/page/475 475] |edition=4th}}</ref> SublimationThe isverb anform [[endothermicof process]]sublimation thatis occurs at temperatures and pressures below a substance's [[triple point]] in its [[phase diagram]]'sublime'', whichor correspondsless to the lowest pressure at which the substance can exist as a liquid. All solids sublimepreferably, though many sublime at extremely low rates that are hardly detectable''sublimate''. The reverse process of sublimation is [[deposition (phase transition)|''deposition'']] or ''desublimation'', in which a substance passes directly from a gas to a solid phase, without passing through the liquid state.<ref name="DepositionDef">{{cite journal |title=Controlling condensation and frost growth with chemical micropatterns |first1=Jonathan B. |last1=Boreyko |first2=Ryan R. |last2=Hansen |first3=Kevin R. |last3=Murphy |first4=Saurabh |last4=Nath |first5=Scott T. |last5=Retterer |first6=C. Patrick |last6=Collier |journal=Scientific Reports |year=2016 |volume=6 |pages=19131 |doi=10.1038/srep19131 |pmid=26796663 |pmc=4726256 |bibcode=2016NatSR...619131B}}</ref> Sublimation has also been used as a generic term to describe a solid-to-gas transition (sublimation) followed by a gas-to-solid transition ([[deposition (phase transition)|deposition]]).<ref>{{Dictionary.com|Sublime}}</ref>

All solids sublime, though most sublime at extremely low rates that are hardly detectable. At [[standard conditions for temperature and pressure|normal pressures]], most [[chemical compound]]s and [[chemical element|elements]] possess three different states at different [[temperature]]s. In these cases, the transition from the [[solid]] to the [[gaseous stategas]] state requires an intermediate liquid state. The pressure referred to is the ''[[partial pressure]]'' of the substance, not the ''total'' (e.g. atmospheric) pressure of the entire system. Thus, any solid can sublimatesublime if its [[vapour pressure]] is higher than the surrounding partial pressure of the same substance, and in some cases, sublimatessublimes at an appreciable rate (e.g. water ice just below 0&nbsp;°C). For some substances, such as [[carbon]] and [[arsenic]], sublimation is much easier than [[evaporation]] from the melt, because the pressure of their [[triple point]] is very high, and it is difficult to obtain them as liquids.

While [[vaporization]] (from liquid to gas) is divided into two types, that occurs as [[evaporation]] on the surface of the liquid, and as [[boiling]] at the boiling point with formation of bubbles in the interior of the liquid, there is no such distinction for the solid-to-gas transition which always occurs as sublimation from in both corresponding cases.

For some substances, such as [[carbon]] and [[arsenic]], sublimation from solid state is much more achievable than [[evaporation]] from liquid state and it is difficult to obtain them as liquids. This is because the pressure of their [[triple point]] in its [[phase diagram]], which corresponds to the lowest pressure at which the substance can exist as a liquid, is very high,

At [[standard conditions for temperature and pressure|normal pressures]], most [[chemical compound]]s and [[chemical element|elements]] possess three different states at different [[temperature]]s. In these cases, the transition from the solid to the [[gaseous state]] requires an intermediate liquid state. The pressure referred to is the ''[[partial pressure]]'' of the substance, not the ''total'' (e.g. atmospheric) pressure of the entire system. Thus, any solid can sublimate if its [[vapour pressure]] is higher than the surrounding partial pressure of the same substance, and in some cases sublimates at an appreciable rate (e.g. water ice just below 0&nbsp;°C). For some substances, such as [[carbon]] and [[arsenic]], sublimation is much easier than [[evaporation]] from the melt, because the pressure of their [[triple point]] is very high, and it is difficult to obtain them as liquids.

Sublimation is an [[endothermic process]]. It is caused by the absorption of heat which provides enough energy for some molecules to overcome the [[intermolecular force|attractive forces]] of their neighbors and escape into the vapor phase. Since the process requires additional energy, it is an [[endothermic]] change. The [[enthalpy of sublimation]] (also called heat of sublimation) can be calculated by adding the [[enthalpy of fusion]] and the [[enthalpy of vaporization]].

The term ''sublimation'' refers specifically to a [[physical change]] of [[state of matter|state]] and is not used to describe the transformation of a solid to a gas in a chemical reaction. For example, the dissociation on heating of solid [[ammonium chloride]] into hydrogen chloride and ammonia is ''not'' sublimation but a chemical reaction. Similarly the combustion of candles, containing [[paraffin wax]], to [[carbon dioxide]] and [[water vapor]] is ''not'' sublimation but a chemical reaction with oxygen.

== Confusions ==

Sublimation is caused by the absorption of heat which provides enough energy for some molecules to overcome the [[intermolecular force|attractive forces]] of their neighbors and escape into the vapor phase. Since the process requires additional energy, it is an [[endothermic]] change. The [[enthalpy of sublimation]] (also called heat of sublimation) can be calculated by adding the [[enthalpy of fusion]] and the [[enthalpy of vaporization]].

While the definition of sublimation is simple, it is often confused as to what counts as a sublimation.

=== False correspondence with vaporization ===

While [[vaporization]] (from liquid to gas) is divided into two types,; that occurs as [[evaporation]]vaporization on the surface of the liquid, andis ascalled [[boilingevaporation]]; and vaporization at the boiling point with formation of bubbles in the interior of the liquid is called [[boiling]], there is ''no'' such distinction for the solid-to-gas transition. whichSolid-to-gas alwaystransition occursis asalways sublimationcalled fromsublimation in both corresponding cases.

=== Misused for chemical reaction ===

The term ''sublimation'' refers specifically to a [[physical change]] of [[state of matter|state]] and is not used to describe the transformation of a solid to a gas in a chemical reaction. For example, the dissociation on heating of solid [[ammonium chloride]] into hydrogen chloride and ammonia is ''not'' sublimation but a chemical reaction. Similarly the combustion of candles, containing [[paraffin wax]], to [[carbon dioxide]] and [[water vapor]] is ''not'' sublimation but a chemical reaction with oxygen.

=== Uncommon definition ===

Sublimation is sometimes used as a generic term to describe a two-step phase transition ― a solid-to-gas transition (sublimation in a more precise definition) followed by a gas-to-solid transition ([[deposition (phase transition)|deposition]]).<ref>{{Dictionary.com|Sublime}}</ref>[[File:Comparison carbon dioxide water phase diagrams.svg|thumb|upright=2|Comparison of phase diagrams of carbon dioxide (red) and water (blue) showing the carbon dioxide sublimation point (middle-left) at 1 atmosphere. As dry ice is heated, it crosses this point along the bold horizontal line from the solid phase directly into the gaseous phase. Water, on the other hand, passes through a liquid phase at 1 atmosphere.]]

==Examples==