Topic: Ice-cream making

One of my friends told me about ice-cream making. He said that the temperature of the ice-cream mixture is lowered by the addition of salt to ice.  This causes the ice-cream mixture to freeze.

If so, then, where does the heat from the ice and ice-cream mixture go? It has to reappear somewhere!
I am totally confused...


Re: Ice-cream making

I think, your doubt should be clear after reading the following explanation.

Freezing point of water (in fact, any liquid) is lowered with an addition of solute to it. Same principle is used for ice-cream making. Freezing point of ice-cream mixture is lower than that of water (i.e. below  0°C). Hence, one cannot make ice-cream with the ice-cream mixture kept surrounded by only pure ice (which is at a temperature of 0°C).

If we add salt to this ice, its freezing point is lowered. Hence at 0°C, ice cannot exist in presence of salt. It tends to melt. But heat content of water at 0°C is more than the heat content of ice at 0°C. (This difference is due to the latent heat.) Hence, it requires additional heat for ice to melt. This heat is extracted from some of the ‘unmelted’ ice and also from the ice-cream mixture. Both these processes lead to lowering of temperature of ice as well as ice-cream mixture. With sufficient quantity of salt added to the ice, the ice-cream mixture is forced to freeze.

So, heat removed is used (as the latent heat) for melting the ice.


Re: Ice-cream making

Oh... So simple... Now I am convinced!