The organization of atoms becomes more structured passing form gas to liquid, to solid. Heat energy is released or absorbed as water changes state. We can measure the loss or gain of sensible heat by measuring temperature changes. However, if the pan initially contained a mixture of water and ice, the temperature would not increase until the ice had melted. Heat is absorbed by the water during the change from ice to water but there would be no corresponding change in temperature until all the ice has melted.
Heat is absorbed as water changes to a less ordered state.
The amount of heat lost or gained per gram of water is expressed in calories of latent heat. The latent heat of fusion , the heat released as water is converted from liquid to solid, is 80 calories per gram of water. The reverse reaction, the conversion of ice to water described above, absorbs 80 calories of heat for each gram of water converted from a solid to a liquid state. Release or absorbtion of latent heat occurs during changes of state in water. Two of these processes, evaporation and condensation, occur over large areas of Earth's surface and contribute significantly to the generation of weather phenomena and the redistribution of heat on the earth's surface.