Latent heat vaporization vs fusion

[SandeshPhy]

Why is the latent heat of vaporisation greater than that of fusion(melting)?
I mean in liquid state,atoms are already far apart, so it must require less energy to make them gas(far apart) as forces(electric in nature) between molecules decrease with distance.

 

[ZealScience]

I don't think that atoms in liquid are far apart. Actually, when solid melts there is small change in density, implying that there isn't quite much change in intermolecular distance. e.g water is virtually densor than ice

 

[SandeshPhy]

I don't think that atoms in liquid are far apart. Actually, when solid melts there is small change in density, implying that there isn't quite much change in intermolecular distance. e.g water is virtually densor than ice

That is only the case for water due to anomalous behavior.
Yes there a change in density from liquid to gas change while there is little from solid to liquid.

 

[ZealScience]

And density of a phase is a god indication of intermolecular distance.

 

[sardar]

The latent heat of vaporization and fusion are both important concepts in thermodynamics that describe the amount of energy required to change the state of a substance from liquid to gas and from solid to liquid, respectively. While the two processes may seem similar, there are key differences that explain why the latent heat of vaporization is greater than that of fusion.

Firstly, it is important to understand that the state of a substance is determined by the arrangement and movement of its molecules. In a solid state, the molecules are tightly packed and vibrate in place, while in a liquid state, the molecules are more mobile and can slide past each other. In a gas state, the molecules are even more spread out and move freely.

In the process of fusion, the molecules within a solid substance must be given enough energy to overcome the attractive forces between them and break free into a liquid state. This requires a significant amount of energy, as the molecules are tightly packed and have strong intermolecular forces holding them together.

On the other hand, in the process of vaporization, the molecules in a liquid state must be given enough energy to overcome not only the attractive forces between them, but also the forces of the surrounding environment. In order to escape into a gas state, the molecules must also overcome the atmospheric pressure above the liquid. This added resistance requires a greater amount of energy, resulting in a higher latent heat of vaporization.

Additionally, as you mentioned, the forces between molecules decrease with distance. In a liquid state, the molecules are already somewhat spread out, making it easier for them to break free into a gas state. In contrast, in a solid state, the molecules are tightly packed, requiring more energy to overcome the strong forces holding them together.

In conclusion, the latent heat of vaporization is greater than that of fusion because it requires more energy to overcome the additional resistance of atmospheric pressure and the already spread out molecules in a liquid state. Moreover, the strong intermolecular forces in a solid state make it more difficult to change the state of a substance, resulting in a higher latent heat of fusion.