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Sublimation is the phase transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.[1] Sublimation is an endothermic process that occurs at temperatures and pressures below a substance's triple point in its phase diagram, which corresponds to the lowest pressure at which the substance can exist as a liquid. The reverse process of sublimation is deposition or desublimation, in which a substance passes directly from a gas to a solid phase.[2] 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).[3] At normal pressures, most chemical compounds and elements possess three different states at different temperatures. 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. So, all solids that possess an appreciable vapour pressure at a certain temperature usually can sublime in air (e.g. water ice just below 0 °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. The term sublimation refers to a physical change of 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. Sublimation is caused by the absorption of heat which provides enough energy for some molecules to overcome the 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.

Contents

1 Examples

1.1 Carbon
Carbon
dioxide 1.2 Water 1.3 Naphthalene 1.4 Other substances

2 Purification by sublimation 3 Historical usage 4 Sublimation predictions 5 See also 6 References 7 External links

Examples[edit]

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.

Carbon
Carbon
dioxide[edit]

Small pellets of dry ice subliming in air

Solid
Solid
carbon dioxide (dry ice) sublimes everywhere along the line below the triple point (e.g., at the temperature of −78.5 °C (194.65 K, −109.30 °F) at atmospheric pressure, whereas its melting into liquid CO2 can occur only along the line at pressures and temperatures above the triple point (i.e., 5.2 atm, −56.4 °C). Water[edit] Snow
Snow
and ice sublime, although more slowly, at temperatures below the freezing/melting point temperature line at 0 °C for most pressures; see line below triple point.[4] In freeze-drying, the material to be dehydrated is frozen and its water is allowed to sublime under reduced pressure or vacuum. The loss of snow from a snowfield during a cold spell is often caused by sunshine acting directly on the upper layers of the snow. Ablation
Ablation
is a process that includes sublimation and erosive wear of glacier ice. Naphthalene[edit] Naphthalene, an organic compound commonly found in pesticide such as mothball also sublimes. It sublimes easily because it is made of non-polar molecules that are held together only by van der Waals intermolecular forces. Naphthalene
Naphthalene
is a solid that sublimes at standard atmospheric temperature[5] with the sublimation point at around 80˚C or 176˚F.[6] At low temperature, its vapour pressure is high enough, 1 mmHg at 53˚C,[7] to make the solid form of naphthalene evaporate into gas. On cool surfaces, the naphthalene vapours will solidify to form needle-like crystals.

Experimental set up for the sublimation reaction of naphthalene Solid naphthalene sublimes and form the crystal-like structure at the bottom of the watch glass

Solid
Solid
compound of naphthalene sublimed to form a crystal-like structure on the cool surface.

Other substances[edit]

Camphor
Camphor
subliming in a cold finger. The crude product in the bottom is dark brown; the white purified product on the bottom of the cold finger above is hard to see against the light background.

Iodine
Iodine
produces fumes on gentle heating. It is possible to obtain liquid iodine at atmospheric pressure by controlling the temperature at just above the melting point of iodine. In forensic science, iodine vapor can reveal latent fingerprints on paper.[8] Arsenic
Arsenic
can also sublime at high temperatures. Purification by sublimation[edit]

Crystals
Crystals
of ferrocene after purification by vacuum sublimation

Sublimation is a technique used by chemists to purify compounds. A solid is typically placed in a sublimation apparatus and heated under vacuum. Under this reduced pressure, the solid volatilizes and condenses as a purified compound on a cooled surface (cold finger), leaving a non-volatile residue of impurities behind. Once heating ceases and the vacuum is removed, the purified compound may be collected from the cooling surface.[9][10] For even higher purification efficiencies a temperature gradient is applied, which also allows for the separation of different fractions. Typical setups use an evacuated glass tube that is gradually heated in a controlled manner. The material flow is from the hot end, where the initial material is placed, to the cold end that is connected to a pump stand. By controlling temperatures along the length of the tube the operator can control the zones of recondensation, with very volatile compounds being pumped out of the system completely (or caught by a separate cold trap), moderately volatile compounds recondensating along the tube according to their different volatilities, and non-volatile compounds remaining in the hot end. Vacuum
Vacuum
sublimation of this type is also the method of choice for purification of organic compounds for the use in the organic electronics industry, where very high purities (often > 99.99%) are needed to satisfy the standards for consumer electronics and other applications. Historical usage[edit] In ancient alchemy, a protoscience that contributed to the development of modern chemistry and medicine, alchemists developed a structure of basic laboratory techniques, theory, terminology, and experimental methods. Sublimation was used to refer to the process in which a substance is heated to a vapor, then immediately collects as sediment on the upper portion and neck of the heating medium (typically a retort or alembic), but can also be used to describe other similar non-laboratory transitions. It is mentioned by alchemical authors such as Basil Valentine
Basil Valentine
and George Ripley, and in the Rosarium philosophorum, as a process necessary for the completion of the magnum opus. Here, the word sublimation is used to describe an exchange of "bodies" and "spirits" similar to laboratory phase transition between solids and gases. Valentine, in his Triumphal Chariot of Antimony (published 1678) makes a comparison to spagyrics in which a vegetable sublimation can be used to separate the spirits in wine and beer.[11] Ripley uses language more indicative of the mystical implications of sublimation, indicating that the process has a double aspect in the spiritualization of the body and the corporalizing of the spirit.[12] He writes:[13]

And Sublimations we make for three causes, The first cause is to make the body spiritual. The second is that the spirit may be corporeal, And become fixed with it and consubstantial. The third cause is that from its filthy original. It may be cleansed, and its saltiness sulphurious May be diminished in it, which is infectious.

Sublimation predictions[edit] The enthalpy of sublimation has commonly been predicted using the equipartition theorem. If the lattice energy is assumed to be approximately half the packing energy, then the following thermodynamic corrections can be applied to predict the enthalpy of sublimation. Assuming a 1 molar ideal gas gives a correction for the thermodynamic environment (pressure and volume) in which pV = RT, hence a correction of 1RT. Additional corrections for the vibrations, rotations and translation then need to be applied. From the equipartition theorem gaseous rotation and translation contribute 1.5RT each to the final state, therefore a +3RT correction. Crystalline vibrations and rotations contribute 3RT each to the initial state, hence −6RT. Summing the RT corrections ; −6RT + 3RT + RT = −2RT.[14] This leads to the following approximate sublimation enthalpy. A similar approximation can be found for the entropy term if rigid bodies are assumed.[15][16]

Δ

H

sublimation

= −

U

lattice energy

− 2 R T

displaystyle Delta H_ text sublimation =-U_ text lattice energy -2RT

See also[edit]

Ablation Dye-sublimation printer, Freezer burn
Freezer burn
– common processes involving sublimation Enthalpy of sublimation Freeze-drying Phase diagram

v t e

Phase transitions of matter

To

Solid Liquid Gas

From Solid — Melting Sublimation

Liquid Freezing — Evaporation

Gas Deposition Condensation —

References[edit]

^ "Sublimate". Merriam-Webster
Merriam-Webster
Dictionary.  ^ Boreyko, Jonathan B.; Hansen, Ryan R.; Murphy, Kevin R.; Nath, Saurabh; Retterer, Scott T.; Collier, C. Patrick (2016). "Controlling condensation and frost growth with chemical micropatterns". Scientific Reports. 6. Bibcode:2016NatSR...619131B. doi:10.1038/srep19131.  ^ "Sublime". Dictionary.com Unabridged. Random House.  ^ Fassnacht, S. R. (2004). "Estimating Alter-shielded gauge snowfall undercatch, snowpack sublimation, and blowing snow transport at six sites in the coterminous USA" (PDF). Hydrol. Process. 18: 3481–3492. Bibcode:2004HyPr...18.3481F. doi:10.1002/hyp.5806. [dead link] ^ Caroll, J. (2014). Natural Gas
Gas
Hydrates. p. 16. ISBN 9780128005750.  ^ Staff writer(s) (2015). "what solid go through sublimation?". National Science Foundation and UCSB School-University partnership. Retrieved 13 November 2015.  ^ Pavia,, D. (2005). Introduction to organic laboratory technique. pp. 781–782. ISBN 0534408338.  ^ Girard, James (2011). Criminalistics: Forensic Science, Crime and Terrorism. Jones & Bartlett Learning. pp. 143–144. ISBN 0-7637-7731-5.  ^ R. B. King Organometallic Syntheses. Volume 1 Transition-Metal Compounds; Academic Press: New York, 1965. ISBN 0-444-42607-8. ^ Harwood, Laurence M.; Moody, Christopher J. (1989). Experimental organic chemistry: Principles and Practice (Illustrated ed.). WileyBlackwell. pp. 154–155. ISBN 0-632-02017-2.  ^ Barrett, Francis (1815). The lives of alchemystical philosophers: with a critical catalogue of books in occult chemistry, and a selection of the most celebrated treatises on the theory and practice of the hermetic art. Macdonald and Son for Lackington, Allen, & Co. p. 233.  ^ DiBernard, Barbara (1980). Alchemy
Alchemy
and Finnegans wake. SUNY Press. p. 57. ISBN 0873953886.  ^ Ripley, George (1591). Compound of Alchemy. ^ Gavezzotti, A. (1997). Theoretical Aspects and Computer Modeling of the Molecular Solid
Solid
State. Chichester: Wiley and Sons.  ^ McDonagh, J. L.; Nath; De Ferrari, Luna; Van Mourik, Tanja; Mitchell, John B. O. (2014). "Uniting Cheminformatics and Chemical Theory To Predict the Intrinsic Aqueous Solubility of Crystalline Druglike Molecules". Journal of Chemical Information and Modeling. 54 (3): 844. doi:10.1021/ci4005805.  ^ McDonagh, James; Palmer, David S.; Van Mourik, Tanja; Mitchell, John B. O. (17 October 2016). "Are The Sublimation Thermodynamics of organic molecules predictable?". Journal of Chemical Information and Modeling. doi:10.1021/acs.jcim.6b00033. ISSN 1549-9596. 

External links[edit]

Media related to Sublimation at Wikimedia Commons

v t e

Separation processes

Processes

Absorption Acid-base extraction Adsorption Chromatography Cross-flow filtration Crystallization Cyclonic separation Dialysis (biochemistry) Dissolved air flotation Distillation Drying Electrochromatography Electrofiltration Filtration Flocculation Froth flotation Gravity separation Leaching Liquid–liquid extraction Electroextraction Microfiltration Osmosis Precipitation (chemistry) Recrystallization Reverse osmosis Sedimentation Solid
Solid
phase extraction Sublimation Ultrafiltration

Devices

API oil-water separator Belt filter Centrifuge Depth filter Electrostatic precipitator Evaporator Filter press Fractionating column Leachate Mixer-settler Protein skimmer Rapid sand filter Rotary vacuum-drum filter Scrubber Spinning cone Still Sublimation apparatus Vacuum
Vacuum
ceramic filter

Multiphase systems

Aqueous two-phase system Azeotrope Eutectic

Concepts

Unit operation

v t e

States of matter (list)

State

Baryonic matter

Solid Liquid Gas
Gas
/ Vapor Plasma

Low energy

Bose–Einstein condensate Fermionic condensate Degenerate matter Quantum Hall Rydberg matter Rydberg polaron Strange matter Superfluid Supersolid Photonic matter

High energy

QCD matter Lattice QCD Quark–gluon plasma Color-glass condensate Supercritical fluid

Other states

Colloid Glass Crystal Liquid
Liquid
crystal Time crystal Quantum spin liquid Exotic matter Programmable matter Dark matter Antimatter Magnetically ordered

Antiferromagnet Ferrimagnet Ferromagnet

String-net liquid Superglass

Transitions

Boiling Boiling
Boiling
point Condensation Critical line Critical point Crystallization Deposition Evaporation Flash evaporation Freezing Chemical ionization Ionization Lambda point Melting Melting
Melting
point Recombination Regelation Saturated fluid Sublimation Supercooling Triple point Vaporization Vitrification

Quantities

Enthalpy of fusion Enthalpy of sublimation Enthalpy of vaporization Latent heat Latent internal energy Trouton's ratio Volatility

Concepts

Binodal Compressed fluid Cooling curve Equation of state Leidenfrost effect Macroscopic quantum phenomena Mpemba effect Order and disorder (physics) Spinodal Superconductivity Superheated vapor Superheating Thermo-diele

.