What does a negative H fusion for a molecule changed phase?

A negative enthalpy of fusion (ΔH_fus) for a molecule indicates that the process of melting, or transitioning from solid to liquid, releases energy. This suggests that the solid state is more stable and has lower energy than the liquid state. As a result, when the solid melts, it requires less energy input to break the intermolecular forces holding the solid together, leading to a release of heat during the phase change. This phenomenon is often observed in substances with strong intermolecular interactions, such as ionic compounds or certain metals.