Question

Why is ΔH_vap for water much greater than ΔH_fus? What does this reveal concerning changes in intermolecular forces in going from solid to liquid to vapor?

Short answer

Most of the hydrogen bonds remains in the liquid phase which must be broken during the transition of liquid to gas phase. For this reason, enthalpy of vaporization(ΔHvap) is much larger than the enthalpy of fusion(ΔHfus) since more intermolecular forces are broken during the vaporization process.

The change in intermolecular forces from solid to liquid is much smaller than that of liquid to vapor.

Step-by-step solution

Explanation

Conversion of solid to liquid is considered as fusion whereas conversion of liquid to gas is known as vaporization. Very few fractions of hydrogen bonds are broken while converting from solid to liquid phase. As a result, most of the hydrogen bonds remains in the liquid phase which must be broken during the transition of liquid to gas phase. For this reason, enthalpy of vaporization(ΔH_vap)is much larger than the enthalpy of fusion(ΔH_fus) since more intermolecular forces are broken during the vaporization process.

The change in intermolecular forces from solid to liquid is much smaller than that of liquid to vapor.