Question

Ice (H2O) melting at 273 K and 1 atm has = 6.01 kJ/mol and = 6.01 kJ/mol while water vaporizing under the same conditions has = 37.6 kJ/mol and = 40.7 kJ/mol. Why is there such a large difference between and , but not for and ?

Answer 1

Answer:

Degree of intermolecular hydrogen bonding

Explanation:

The energy required to melt a solid substance and the temperature at which the solid melts depends on the structure of the solid crystal as also on the magnitude of the intermolecular forces present in the solid.

Ice is less dense than liquid water, there are spaces in the crystal structure of ice. Secondly, the magnitude of hydrogen bonding in ice is lower due to lower intermolecular interaction between the water molecules. Given the lower intermolecular interaction in ice, the heat of fusion is much lower since the intermolecular interactions are easier to break.

In liquid water, hydrogen bonding is much stronger and there is greater intermolecular interaction between the water molecules. It takes more energy to break down these intermolecular interactions, hence the high enthalpy of vaporization of liquid water.