What is the heat of fusion associated with?

The heat of fusion refers specifically to the energy required to change a substance from a solid to a liquid at its melting point, without changing its temperature. This process involves breaking the intermolecular forces that hold the solid particles in a fixed position, allowing them to move freely as a liquid. During this transition, the temperature of the substance remains constant, as all the added thermal energy is used to overcome these intermolecular forces rather than increasing the temperature.

In contrast, boiling involves the conversion of a liquid to a gas (the heat of vaporization), condensation refers to the process where a gas turns back into a liquid, and sublimation is the transition from a solid directly to a gas. Each of these processes has its own distinct energy requirements and processes involved, which are different from the melting process associated with the heat of fusion. Thus, the correct association of heat of fusion is with melting.