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The Challenge: Make Ice

Heat Transfer

So, if we are going to freeze our water to make ice, we will need to slow the water molecules down by removing energy to the point where the hydrogen bonds can hold the molecules closely together in a lattice.

The First Law of Thermodynamics says that energy cannot be created or destroyed, only converted from one form to another. We can remove energy from the water by placing it in contact with something cold. We'll be using a cooling liquid.

Conduction transfers heat between the water and the cooling liquid. We don't want to contaminate the water with the cooling liquid so we keep them separate by putting the cooling liquid inside a container. The container then sits in the water.

Heat transfer diagramEnergy from the water is transferred through the walls of the container to the cooling liquid.

This is all in accordance with The Second Law of Thermodynamics.

We need to make sure that as we 'suck' heat out of the water and into our cooling liquid, we don't get more heat creeping into the water from outside the container. If we use a cup made of polystyrene as the container, it will insulate the water and prevent any more heat from getting in.