Why does vaporizing water require more energy than melting ice?

Vaporizing water requires significantly more energy than melting ice because of the fundamental differences in the molecular changes required for each phase transition.

When ice melts into liquid water, energy—known as the latent heat of fusion—is required to break the rigid, ordered crystalline solid lattice structure. This process allows the molecules to move more freely while still maintaining the cohesive forces characteristic of the liquid state.12

In contrast, converting liquid water into a gaseous state requires the latent heat of vaporization to completely overcome the hydrogen bonds and other intermolecular forces that hold the liquid together. Because the gaseous phase involves molecules becoming largely independent and occupying a much larger volume, the energy input needed to break these remaining cohesive forces is substantially higher than that required to simply transition from a solid to a liquid. For instance, at normal pressure, it takes approximately 80 calories per gram to melt ice, whereas it takes about 540 calories per gram to vaporize liquid water.1234