I am wondering whether there is an element in the periodic table which would go in reverse through the three stages of matter, gas to solid, as the temperature rises?
Posted Jul 19, 2016, 9:33 AM UTC
The states of matter are not only influenced by the temperature. The pressure influences it too. That is, for example, the reason why the boiling point of water gets lower when you get on higher altitudes with less atmospheric pressure. It's also the reason why the core of the earth is solid, while it has about 5000°C
Matter can indeed go from gas over liquid to solid while you heat it, but only if you apply more and more pressure on it. Those pressures will become extremely intense, though. We're talking about thousands of bar, depending on the matter and temperature.
Let's take water as an example.
At -78°C and 101,3 kPa it's gas. Now we heat it to -55°C and increase the pressure to 520 kPa and it's fluid. Now we heat it to -50°C and apply several MPa and it'll become solid.
[removed]
[removed]
[removed]
[removed]
My practical interpretation is, in short, no. Or has not been observed.
Based on Kinetic Theory, the temperature is the average kinetic energy of the atoms. The higher the kinetic energy, the higher the temperature. Gases are implied to have a high kinetic energy than solids since gases retain the ability to freely collide and move past one another whereas solids cannot.
Such a state may exist for some exotic condition on a triple phase diagram but in practical everyday cases, it is super unlikely (and has not been observed).
The closest thing I can think off the top of my head that is related to your question is that water expands as it freezes, but the temperature is still inherently lower.
Such an element would violate the laws of thermodynamics. If we look at the two extreme cases we can see why.
At absolute zero, there is no energy available to a system of molecules to move about. Intermolecular attractions (present for any element) will naturally bring the molecules together. This will necessarily lead to a solid phase.
At sufficiently high temperature, entropy will always lead to preferential formation of a gas phase. Because a gas is inherently more disordered than a solid, it will always be the entropically favored phase, despite solids and liquids being favored energetically.
In essence, the reasons for the general trend: solid->(liquid)->gas at a given pressure are more fundamental than the behavior of individual elements, so you would not expect to find exceptions in the periodic table.