Question

Explain the latent heat of melting on the basis of molecular model of solution

Answer 1

The kinetic theory says that temperature is the measure of the average kinetic energy. That would mean then: The temperature rises with the rise in kinetic energy. We know that when matter changes state 'latent heat' helps in 'breaking the bonds' at the transition phase and that this 'extra heat' is not noticed on a thermometer. But energy can neither be made nor destroyed. Taking that into consideration latent heat has to convert into some form of energy. Since temperature is not rising, it's not kinetic energy it's getting converted to.

Answer 2

down vote

Experimentally heat is absorbed to melt a solid or to vaporise a liquid and as the temperature remains constant at the melting or boiling temperature, the entropy must be increasing. If the entropy change from one phase to the other is ΔS1,2=S2−S1ΔS1,2=S2−S1 and the heat absorbed (i.e. enthalpy or latent* heat) is positive ΔH1,2ΔH1,2 in transforming phase 1 to phase 2, the entropy change is positive,ΔS1,2=ΔH1,2/TΔS1,2=ΔH1,2/T.

Any solid or liquid is held together by intermolecular potential energy, in general called van-der-Waals potentials (ion-dipole, dipole - dipole etc). Starting from a temperature just below the melting point as energy is added the molecules absorb this both as kinetic and potential energy (vibration and rotation quantum numbers increase) both internally (normal mode vibrations & rotations) and also as motion in the intermolecular potential.