Melting Point: How Heat Changes Liquids to Solids

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Discussion Overview

The discussion revolves around the conditions under which a substance can transition from a liquid state to a solid state upon heating, particularly focusing on whether this can occur without chemical change. Participants explore examples, theoretical possibilities, and the implications of entropy in phase transitions.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants assert that no substance can change from liquid to solid upon heating without undergoing a chemical change.
  • Others mention ceramics as an example where a liquid structure transitions to a solid structure, but this involves bond formation during heating.
  • Concrete is cited as a potential example, but it is noted that its transition involves a chemical reaction.
  • A question is raised about the possibility of a solid solution having a liquid phase at a lower temperature than a solid phase, suggesting that this could occur if the high-temperature solid phase has higher entropy than the liquid phase.
  • One participant recalls that such reversible transformations have been observed in specially designed polymer systems, indicating that this phenomenon might be rare but possible.
  • References to literature are made, including a study by Plazanet et al. that discusses freezing on heating of liquid solutions, although it is noted that the underlying physics is still being explored.
  • There is a distinction made between single-component and multi-component systems in relation to phase changes.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether a substance can change from liquid to solid upon heating without chemical change. Multiple competing views remain, particularly regarding examples and theoretical possibilities.

Contextual Notes

The discussion highlights limitations in understanding phase transitions, particularly regarding the definitions of chemical change and the conditions under which different phases can exist. The complexities of multi-component systems versus single-component systems are also noted.

sam013024
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Name a substance that will change from liquid state to solid state on heating.
 
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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.
 
eggy-weggy :biggrin:
 
Bloodthunder said:
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?
 
QuantumPion said:
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.
 
tiny-tim said:
eggy-weggy :biggrin:

You read my mind. :biggrin:
 
Changes chemically :)
 
tiny-tim said:
eggy-weggy :biggrin:

Like!
 
Mapes said:
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.
 
Last edited by a moderator:
  • #10
Mapes said:
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.
 
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  • #11
QuantumPion said:
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.
 

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