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Old Jul 7th 2014, 06:08 PM   #1
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A gas close to zero Kelvin

Consider an adiabatic expansion of an ideal gas that work is done against friction or a piston. Since no heat exchange can occur the gas keep on losing energy and its temperature decreases and the gas molecules getting further and further apart. In principle the temperature can get down to a few degrees Kelvin, close to zero K.

Is it possible that a gas can still be a gas at such a low temperature?
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Old Jul 8th 2014, 06:10 AM   #2
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This is indeed a method for creating super-cold gasses. But no gas is truly an "ideal" gas, and so there is a limit to this. Hydrogen for example tirns to liquid at about 28 Kelvin. To get temps below that yuo ned other techniques for extracting heat, such as using lasers to trap individual atoms to keep them from moving.
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Old Jul 9th 2014, 03:56 AM   #3
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The transition from gas to liquid depends on both the temperature and pressure.
However, to remain a gas at super low temperatures the pressure would have to be super low.
When the pressure gets this low, it is debateable if you still have a gas or just a collection of disassociated atoms.
A gas implies that there are interactions and attractions between the atoms, but that thier motion (which is their temperature) keeps them from being a liquid.

When the temperatures get into the milli-kelvin, then terms like liquid and gas start to loose their applicability.
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Old Jul 9th 2014, 06:04 PM   #4
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Thanks both.
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