Heat absorbed or released as the result of a phase change. There are three basic types of latent heat each associated with a different pair of phases: Process in which two lighter atomic nuclei combine to form a heavier atomic nucleus. Very high temperatures are normally required in order for atomic nuclei to collide with sufficient energy to overcome the Coulomb barrier (their mutual electrostatic repulsions). Fusion that occurs under high-temperature conditions is called thermonuclear fusion. Fusion (solid-liquid), vaporization (liquid-gas), and Process in which a material changes from a frozen solid to a gas without passing through the liquid state. Whether a material will sublimate, melt, or vaporize depends on the temperature and pressure of its environment. For example, if the pressures are low enough, water ice will turn directly into (solid-gas). No temperature change occurs during a phase change, thus there is no change in the kinetic energy of the particles in the material. The energy released comes from the potential energy stored in the bonds between the particles. Processes may either release or absorb latent heat. A chemical reaction that is accompanied by or requires the absorption of energy from its environment. A classic endothermic reaction is the melting of ice cubes in a cup of water. phase changes absorb heat from the environment and are cooling processes. A chemical or nuclear reaction that liberates heat energy so that heat flows from the system to the surroundings. Exothermic reactions cause an increase in temperature. A classic exothermic reaction is the mixing of a strong acid with water. In order to prevent an explosive and dangerous reaction, the acid phase changes release heat to the environment and are warming processes. Transformations between pairs of phases are given different names depending upon whether the process is endothermic or exothermic. For example, the solid-liquid phase change may be called melting or fusion (endothermic) or Physical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals., freezing or solidification (exothermic).
Some or all content above used with permission from J. H. Wittke.