Faza (termodinamika) – razlika između verzija
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Red 6:
Termin ''faza'' se ponekad koristi kao sinonim za [[Agregatna stanja|agregatno stanje materije]], mada može da postoji nekoliko faza koje se ne [[Mešljivost|mešaju]], iako su u istom agregatnom stanju. Isto tako, termin ''faza'' se ponekad koristi za označavanje skupa ravnotežnih stanja razdvojenih [[faznim granicama]] na [[fazni dijagram|faznom dijagramu]] izraženih u vidu promenljivih stanja, kao što su pritisak i temperatura. Pošto se fazne granice odnose na promene u organizaciji materije, kao što su promene od tečnog do čvrstog stanja, ili na suptilnije promene jedne kristalne strukture u drugu, ovaj drugi vid primene je sličan primeni "faze" kao sinonima za stanje materije.
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{{glavni|Fazni dijagram}}
[[File:Steel pd.svg|thumb|left|350px|Iron-carbon [[phase diagram]], showing the conditions necessary to form different phases]]
Različite faze sistema mogu se predstaviti korištenjem '''faznih dijagrama'''. Ose dijegrama su relevantne termodinamičkim varijablama. Za jednostavne mehaničke sisteme, obično se koriste [[pritisak]] i [[temperatura]].
Distinct phases may also exist within a given state of matter. As shown in the diagram for iron alloys, several phases exist for both the solid and liquid states. Phases may also be differentiated based on [[solubility]] as in polar (hydrophilic) or non-polar (hydrophobic). A mixture of water (a polar liquid) and oil (a non-polar liquid) will spontaneously separate into two phases. Water has a very low [[solubility]] (is insoluble) in oil, and oil has a low solubility in water. Solubility is the maximum amount of a solute that can dissolve in a solvent before the solute ceases to dissolve and remains in a separate phase. A mixture can separate into more than two liquid phases and the concept of phase separation extends to solids, i.e., solids can form [[solid solution]]s or crystallize into distinct crystal phases. Metal pairs that are mutually soluble can form [[alloy]]s, whereas metal pairs that are mutually insoluble cannot.
As many as [[multiphasic liquid|eight immiscible liquid phases]] have been observed.<ref>One such system is, from the top: mineral oil, silicone oil, water, aniline, perfluoro(dimethylcyclohexane), white phosphorus, gallium, and mercury. The system remains indefinitely separated at {{val|45|u=°C}}, where gallium and phosphorus are in the molten state. From {{cite book
|author=Reichardt, C.
|date=2006
|title=Solvents and Solvent Effects in Organic Chemistry
|pages=9–10
|publisher= Wiley-VCH
|isbn=3-527-60567-3
}}</ref> Mutually immiscible liquid phases are formed from water (aqueous phase), hydrophobic organic solvents, perfluorocarbons ([[organofluorine chemistry#Fluorous phases|fluorous phase]]), silicones, several different metals, and also from molten phosphorus. Not all organic solvents are completely miscible, e.g. a mixture of [[ethylene glycol]] and [[toluene]] may separate into two distinct organic phases.<ref>This phenomenon can be used to help with catalyst recycling in Heck vinylation. See {{cite journal
|author=Bhanage, B.M.
|display-authors=etal
|date=1998
|title=Comparison of activity and selectivity of various metal-TPPTS complex catalysts in ethylene glycol — toluene biphasic Heck vinylation reactions of iodobenzene |journal = Tetrahedron Letters
|volume=39 |issue=51 |pages=9509–9512
|doi=10.1016/S0040-4039(98)02225-4
}}</ref>
Phases do not need to macroscopically separate spontaneously. [[Emulsion]]s and [[colloid]]s are examples of immiscible phase pair combinations that do not physically separate.
== Fazna ravnoteža ==
Left to equilibration, many compositions will form a uniform single phase, but depending on the temperature and pressure even a single substance may separate into two or more distinct phases. Within each phase, the properties are uniform but between the two phases properties differ.
Water in a closed jar with an air space over it forms a two phase system. Most of the water is in the liquid phase, where it is held by the mutual attraction of water molecules. Even at equilibrium molecules are constantly in motion and, once in a while, a molecule in the liquid phase gains enough kinetic energy to break away from the liquid phase and enter the gas phase. Likewise, every once in a while a vapor molecule collides with the liquid surface and condenses into the liquid. At equilibrium, evaporation and condensation processes exactly balance and there is no net change in the volume of either phase.
At room temperature and pressure, the water jar reaches equilibrium when the air over the water has a humidity of about 3%. This percentage increases as the temperature goes up. At 100 °C and atmospheric pressure, equilibrium is not reached until the air is 100% water. If the liquid is heated a little over 100 °C, the transition from liquid to gas will occur not only at the surface, but throughout the liquid volume: the water boils.
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