Sublimation is the phase transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. 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. 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). 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.
2 Purification by sublimation 3 Historical usage 4 Sublimation predictions 5 See also 6 References 7 External links
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.
Small pellets of dry ice subliming in air
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
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. 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.
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 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. This leads to the following approximate sublimation enthalpy. A similar approximation can be found for the entropy term if rigid bodies are assumed.
− 2 R T
displaystyle Delta H_ text sublimation =-U_ text lattice energy -2RT
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Phase transitions of matter
Solid Liquid Gas
From Solid — Melting Sublimation
Liquid Freezing — Evaporation
Gas Deposition Condensation —
Media related to Sublimation at Wikimedia Commons
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Dissolved air flotation
API oil-water separator
Rapid sand filter
Rotary vacuum-drum filter
Aqueous two-phase system Azeotrope Eutectic
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States of matter (list)
Bose–Einstein condensate Fermionic condensate Degenerate matter Quantum Hall Rydberg matter Rydberg polaron Strange matter Superfluid Supersolid Photonic matter
QCD matter Lattice QCD Quark–gluon plasma Color-glass condensate Supercritical fluid
Antiferromagnet Ferrimagnet Ferromagnet
String-net liquid Superglass
Enthalpy of fusion Enthalpy of sublimation Enthalpy of vaporization Latent heat Latent internal energy Trouton's ratio Volatility
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