# Latent heat and colligative properties

1. Jul 17, 2010

### johnuk

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

2. Jul 19, 2010

### johnuk

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 Â£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. Jul 20, 2010

### johnuk

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.