Melting Point: How Heat Changes Liquids to Solids

In summary: Right, or put another way, a multi-component system (with additional factors such as mutual solubility)
  • #1
sam013024
1
0
Name a substance that will change from liquid state to solid state on heating.
 
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  • #2
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.
 
  • #3
eggy-weggy :biggrin:
 
  • #4
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?
 
  • #5
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.
 
  • #6
tiny-tim said:
eggy-weggy :biggrin:

You read my mind. :biggrin:
 
  • #7
Changes chemically :)
 
  • #9
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" [Broken]. But a look at the subsequent literature indicates that the physics is still being worked out.
 
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  • #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" [Broken]. 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.
 

1. What is melting point?

Melting point is the temperature at which a solid substance changes to a liquid state. It is the temperature at which the molecules of a substance have enough energy to overcome their attractive forces and move freely as a liquid.

2. How does heat affect the melting point of a substance?

As heat is added to a substance, the molecules gain more energy and begin to vibrate faster, causing the attractive forces between them to weaken. This results in a lower melting point, meaning the substance will change from a solid to a liquid at a lower temperature.

3. Why is melting point an important characteristic of a substance?

The melting point of a substance is a unique physical property that can help identify and distinguish it from other substances. It can also provide information about the purity of a substance, as impurities can affect the melting point.

4. Can the melting point of a substance change?

Yes, the melting point of a substance can change depending on external factors such as pressure and the presence of impurities. However, the melting point of a pure substance remains constant under standard conditions.

5. How is the melting point of a substance determined?

The melting point of a substance can be measured using a variety of methods, including melting point apparatus, differential scanning calorimetry, and capillary tube method. These methods involve heating the substance and recording the temperature at which it changes from a solid to a liquid.

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