Heat energy can change the phase of the matter. Matter can exist in different phases, including solid, liquid and gases. These phases are differentiated based on (among other things) the kinetic energy of the molecules. The constituent molecules are very tightly bound in a solid and hence have low kinetic energy, as compared to a gaseous phase, in which all the molecules have very high kinetic energies. When we heat a material, its molecules gain kinetic energy and this induces phase change. For example, when we heat ice (solid phase of water), it converts to water (liquid phase), resulting in increased kinetic energy of water molecules. Further heating converts water to water vapor (gas phase) with a corresponding increase in molecules' kinetic energy. Heat energy can also directly convert some materials from solid to a gaseous phase (in a process called sublimation).
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