Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: cuso4 on 26/04/2004 08:24:51
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What's the difference between phase and state? And which terminology should be used?
Angel
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Phase indicates the structural composition of the material...solid, liquid, gas, or "other." (where other=Bose-Einstein condenstate or other rarely achieved phase of matter)
State is a thermodynamic concept and would include phase as well as all other properties like temperature, pressure, volume, and chemical potential.
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Thanks Jay. My teacher said that there are also aqueous and organic phase.
Angel
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I should have been more clear on phase....phase can also mean different types of the same phase. Confused? [:D]
For instance, if you have 3 liquids in a test tube that are immiscible so that they for 3 different layers, then you can say that there are 3 phases present. (like your teacher said, organic vs aqueous phase, but obviously you'd be more specific if there are 3 phases present)
If the substances mix, however, it's considered one phase. Let's say you have a container with a gas mixture of ether/water vapor above an ether layer that is floating on top of a water layer containing dissolved NaCl and sitting in the bottom of the container is a lump of undissolved solid NaCl. How many phases is that? If you said 4, you'd be right. The gas mixture is considered one phase. The ether later is a phase, the water layer is a phase, and the solid lump is a phase.
Hope that clears it up more.
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whats a bose-einstein condensate? similar to a super-critical fluid??
We don't want the loonies taking over!
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Basically, it's a state of matter obtained at VERY low temperatures where all of the atoms making up the condensate exist in the same quantum state...they basically behave as one giant atom. You can probably find a much better and more in-depth description with a quick google search. It's more physics than chemistry, not my forte by a long shot.
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A super-critical fluid is a phase of matter between liquid and gas. It behaves like a dense gas, and a light fluid at the same time. CO2 has such a phase, above 85 degrees F, and about 1200 psi. It is used as a cleaning fluid when supercritical. There are many other phases present in nature. Ferromagnetism is a phase of matter; it disappears above the Curie temperature of the material. Helium III is another phase- its a superfluid, a Bose-Einstein condensate. The bound-state of quarks in protons and neutrons is a phase of matter. At extremely high pressure and temperature, this phase changes to an unbound state. The coulombic phase of electrons is another one. There are many examples. The study of critical-point phenomena is a branch of physics.
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Actually wouldn't it be more correct to say that a super critical fluid is beyond liquid and gas, not between? Between sounds to me like somewhere on the liquis/gas phase line which would only result in a combination of the two states. Probably just a matter of semantics, but I don't want people to be confused as to what it is, because I personally find them very interesting
We don't want the loonies taking over!
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A super-critical fluid is a fluid with 'properties' between liquid and gas. On a phase diagram, the super-critical phase would be distinct from either the liquid or gas phases, and would not lie on any lines between them. However, the properties of the super-critical phase vary greatly over its range of pressure and temperature. At one extreme, it is nearly liquid, and at the other it is nearly gas. It is worth noting that the 'state' of the super-critical phase is determined by its thermodynamic 'state variables', of pressure and temperature.
OBTW, I typoed the super-fluid helium phase remark. Below 2 K, the isotope of helium known as helium-4, becomes a super-fluid, where it is known as helium II (NOT III). It is a Bose-Einstein condensate, and has the most amazing and baffling properties. It illustrates quantum mechanical properties on a macroscopic scale.
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Hi,
Back to the old topic,
my teacher said that as a gas, even when we have 2 or more substances, we consider as 1 phase only, but he also said that in physics it would be consider as 2 phases or more.
Why have the difference?
Chemistry is my love
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I'm not sure why physicists treat multiple gases as separate phases. Chemists treat it as one phase because a gas mixture is going to have the same properties in any average region of the overall gas phase. Say you have a separatory funnel containing both ether and water. The water and ether layers are going to be separate, and each count as one phase. The gas layer over the top of both is going to contain both ether and water vapor and, assuming no changes to the system, will maintain a constant composition, hence is considered one phase.
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