How do additives in ice change Latent Heat of Fusion?

[EngSci]

When using ice to keep a room (or in my case, a cooler) cold, one would want it to have a high specific heat capacity and a high latent heat of fusion, so that it would absorb a lot of energy as it melts. Basically, so that it melts as slowly as possible.

I know that adding salt to road ice will lower the melting point of the ice, making it melt faster. But what if you were to mix salt with water and then freeze it? To me it would make sense that the ice melts sooner than ice made from pure water, because of the lower melting point. However, after doing some research I've found that the opposite is true, and that salt-ice takes longer to melt than water ice.

Why does this happen? If KCl was used instead of NaCl, would that make the ice melt more slowly, or less slowly? What substances would you add to ice in order to make it melt as slowly as possible?

Thanks for the help.

 

[jbsteele]

The reason that salt-ice takes longer to melt than water ice is because when the salt and water are mixed together, the salt particles increase the number of molecules in the solution, which makes it harder for the ice to absorb heat. This is because the molecules of the salt compete with the water molecules for the heat energy and the water molecules can't absorb the heat as quickly.Using KCl instead of NaCl will not make much of a difference since both salts have similar properties. To make the ice melt as slowly as possible, you would need to add a substance with a high specific heat capacity, such as glycerol, or a high latent heat of fusion, such as calcium chloride. Both of these substances have the ability to absorb large amounts of heat energy and thus keep the ice from melting quickly.