Question

Why are m.p. and b.p. of heavy water more than those of ordinary water?

Answer 1

Answers. The hydrogen bonds in deuterium oxide are slightly stronger than those in water. This is due to a quantum mechanical effect; the bonding interaction has a lower zero point energy due to the greater mass of the deuterium atom

Answer 2

The melting point and of heavy water is more than those of ordinary water. It is because the “bond dissociation enthalpy” of the heavy water is high. It needs high temperature and pressure to break the single bond present in the heavy water. On the same time, the normal water can be “easily dissociated” at less pressure and temperature. The melting and boiling point of hydrogen (normal water) is 13.96 K and 20.39 K respectively while it is 18.73 K and 23.67 K in case of heavy water.