crystallization is the quantity of heat which needs to be removed from a unit weight of liquid for it to become a solid. As melting and crystallization occur, the faster, higher kinetic energy molecules enter or remain in the liquid state, while the slower, lower kinetic energy molecules remain or enter the solid state.
Some solids, such as snow and ice, melt at temperatures below their melting points, indicating that some of their molecules have sufficient energy to enter directly into the vapor phase (Sisler, VanderWerf and Davidson, 1967, 64). Solids such as camphor and naphthalene give off odors which can be detected some distance away from the solids, which means that molecules with greater kinetic energy can break away from the surface of these solids directly into the vapor phase. The vapor pressure of a solid is the pressure exerted by the vapor in equilibrium with the solid at that temperature. Solids such as iodine and dry ice, which have very weak forces binding the molecules, have measurable vapor pressures at room temperature. Increa
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