Latent heat and colligative properties

In summary, the table in the CRC Handbook lists latent heats of fusion, vaporization, and sublimation as well as their corresponding temperatures. However, it is not clear if the heat capacities change with increasing solute concentration. Putting salt into water does not seem to increase the latent heat capacity of the resulting compound solid.
  • #1
johnuk
7
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I have a couple of questions about this. I know what it is, but need information on specific values.

I've been trying to find a table listing as many compounds as possible by their latent heat capacity. I'm also interested in their approximately melting point and would prefer them both in the same table. At the moment, I'd settle for just the latent heats.

I've been googling for half an hour or more and not found much. MatLab isn't that helpful either.

Does anyone know where there hides an absolutely stonkingly massive list of them? I'm not particularly after the periodic table versions, but compounds.

Also, does anyone know how the latent heat capacity of something changes as more solute is added? I know this is called a colligative property of a solution and that I can calculate the depression in a freezing point. What interests me is, does the latent heat capacity of the solution change as well?

To put this into the real world, I'm trying to make something very cold and stay very cold for as long as possible. Phase change media and gel packs all have about the same latent heat capacity of water.

The lowest my freezer will go is -18C, and phase changes generally have higher heat capacities than the gel packs.

So my first thought is, pour salt into water until I have about enough that it'll freeze just around -18C, which is about 580g per litre I think.

Now I'm wondering, does doing so increase the latent heat capacity of my new compound solid?

And, as high as the latent heat capacity of ice is, I'm curious to know if something else has even more.

Thanks for reading and thank you for any help!
John
 
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  • #2
Bump, still searching, still haven't found one.

The only possible location of one a good one is in the CRC Handbook of Chemistry and Physics, but I need an athens account to look at that or to buy a copy at £83.

Does anyone have an athens? Could you have a look and see what the tables look like? They'll probably be listed as 'enthalpy of fusion'. It says there's over a thousand hits for that.
 
  • #3
I found one, there's a gigantic table in the CRC Handbook I mentioned.

I also tried a few experiments, putting various concentrations of salt / ethylene glycol into water and freezing them. Almost none of the salt ones actually froze, despite the concentrations being theoretically low enough. The salt would simply drop out of solution to a large extent.

Two of the EG ones did freeze to some degree, forming a large crystal based hard slush or something like a slush puppy. The temperatures of these did remain lower than my pure ice sample for longer (which rapidly went to 0C), but they also went through a specific heat capacity change in this region, not a latent heat change; e.g. they 'warmed up' rather than melting. They also went to a runny slush in not very long at all, whilst the ice remained at 0C and with most of it intact.
 

FAQ: Latent heat and colligative properties

1. What is latent heat?

Latent heat is the amount of heat energy required to change the state of a substance without changing its temperature. This energy is used to break or form intermolecular bonds between molecules.

2. What are colligative properties?

Colligative properties are physical properties of a solution that depend only on the number of solute particles present, rather than the type of solute. These properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.

3. How does latent heat affect colligative properties?

Latent heat plays a role in colligative properties because it is involved in the phase changes that occur when solutes are added to a solvent. For example, when solutes are added to a solvent, it takes more energy to raise the boiling point or lower the freezing point due to the intermolecular bonds that must be broken.

4. What is the relationship between the number of solute particles and colligative properties?

The more solute particles present in a solution, the greater the colligative effect will be. This is because there are more particles available to disrupt the intermolecular bonds and affect the physical properties of the solution.

5. How do colligative properties impact real-world applications?

Colligative properties have practical applications in many industries, such as in food preservation (freezing point depression), antifreeze for cars (freezing point depression), and the production of pharmaceuticals (osmotic pressure). Understanding and manipulating these properties can also help in the development of new materials and technologies.

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