Melting Point: How Heat Changes Liquids to Solids

[sam013024]

Name a substance that will change from liquid state to solid state on heating.

 

[Bloodthunder]

And remaining chemically unchanged? Nothing does that.

You could have your ceramics which change from a liquid structure to a solid structure, but that's with the formation of bonds on heating and all that.

 

[tiny-tim]

eggy-weggy

 

[QuantumPion]

And remaining chemically unchanged? Nothing does that.

You could have your ceramics which change from a liquid structure to a solid structure, but that's with the formation of bonds on heating and all that.

The first thing that came to my mind was concrete, but that is a chemical reaction and doesn't really count.

Is it possible for some sort of solid solution to have a liquid phase at a lower temperature than a solid phase? E.g. one component of the solution precipitates out with increasing temperature while the other component turns to liquid?

 

[Mapes]

Is it possible for some sort of solid solution to have a liquid phase at a lower temperature than a solid phase?

It is possible, even for reversible transformations. It's only required that the high-temperature phase (the solid) has a higher entropy than the low-temperature phase (the liquid). As you can imagine, this is pretty unusual. I seem to remember that it's been demonstrated in some carefully designed polymer systems, though. Will look to see if I can find the details.

 

[DaveC426913]

eggy-weggy

You read my mind.

 

[Bloodthunder]

Changes chemically :)

 

[Andy Resnick]

eggy-weggy

Like!

 

[Mapes]

It is possible, even for reversible transformations. It's only required that the high-temperature phase (the solid) has a higher entropy than the low-temperature phase (the liquid). As you can imagine, this is pretty unusual. I seem to remember that it's been demonstrated in some carefully designed polymer systems, though. Will look to see if I can find the details.

Ah, I found it: Plazanet et al., "Freezing on heating of liquid solutions," J Chem Phys 121:5031 p5031 (2004), discussed http://physicsworld.com/cws/article/news/20325" . But a look at the subsequent literature indicates that the physics is still being worked out.

 

[QuantumPion]

Ah, I found it: Plazanet et al., "Freezing on heating of liquid solutions," J Chem Phys 121:5031 p5031 (2004), discussed http://physicsworld.com/cws/article/news/20325" . But a look at the subsequent literature indicates that the physics is still being worked out.

Interesting, although it sounds like that is still just a chemical reaction, although notably a reversible one.

 

[Mapes]

Interesting, although it sounds like that is still just a chemical reaction

Right, or put another way, a multi-component system (with additional factors such as mutual solubility) rather than a single-component system.