Refrigeration

When a substance changes state—that is, when a solid melts to a liquid or a liquid turns to a gas, or vice versa—there is a considerable transfer of heat energy. For example, when ice melts, a lot of heat has to pass into it to allow it to change to water. This heat is drawn in from the surroundings, so anything in contact with the melting ice loses heat and becomes colder. All the available heat is going into the melting process, so the ice and its meltwater remain at freezing point until all the ice has melted, and only then do things start to warm up.