Phase Transitions
When a substance undergoes a phase transition (changes from one state of matter to another) it usually either takes up or releases energy. For example, when water evaporates, the kinetic energy expended as the evaporating molecules escape the attractive forces of the liquid is reflected in a decrease in temperature. The amount of energy required to induce the transition is more than the amount required to heat the water from room temperature to just short of boiling temperature, which is why evaporation is useful for cooling. See Enthalpy of vaporization. The reverse process, condensation, releases heat. The heat energy, or enthalpy, associated with a solid to liquid transition is the enthalpy of fusion and that associated with a solid to gas transition is the enthalpy of sublimation.
Read more about this topic: Phase (matter)
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