Heat of fusion, also called enthalpy of fusion or latent heat of fusion, is the amount of thermal energy required to change a given quantity of a substance from a solid to a liquid state at its melting point, without any change in temperature. This energy is absorbed to overcome the intermolecular forces holding the molecules in their rigid, ordered solid structure, allowing them to move more freely as a liquid. Conversely, the same amount of energy is released when a liquid solidifies or freezes at its freezing point. For example, when ice melts at 0°C, it absorbs a specific amount of heat to become liquid water at 0°C, its temperature only begins to rise after all the ice has completely melted. This unique characteristic, where heat is absorbed or released without a corresponding temperature change during a phase transition, is why it's referred to as latent heat. The heat of fusion is a crucial physical property for various applications, including metallurgy, cryogenics, and understanding natural phenomena like the melting of glaciers.
