Energetics of Melting and Freezing

The most common way to cool down a drink is to drop several ice cubes into it. As the ice melts, the drink cools because melting is endothermic—heat is absorbed 

A FIGURE 12.16 Heating curve during melting A graph of the temperature of ice as it is heated from -20 °C to 35 °C. During melting, the temperature of the solid and the liquid remain at 0 °C imtil the entire solid is melted. 

Freezing, the opposite of melting, is exothermic— heat is released when a liquid freezes into a solid. For example, as water in your freezer turns into ice, it releases heat, which must be removed by the refrigeration system of the freezer. If the refrigeration system did not remove the heat, the water would not completely freeze into ice. The heat released as it began to freeze would warm the freezer, preventing further freezing. 

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