Heat of vaporisation help please

[Benzeen]

Hi, i am writing a assignment about thermal expansion and contraction
and i would like to know if anyone could explain to me why the heat of vaporisation is nearly seven times that of the heat of fusion for water. I thought it might be hydrogen bonding but this is present in both the liquid and solid phases. any help is appreciated

 

[snshusat161]

To convert ice to water not much energy is needed because there is not much change. Only the bonds or attractive force get weaker but molecules are still close together but in vapor phase molecules gains so much of kinetic energy that they are free to move all around the spaces and so we need to give much more energy.

 

[Benzeen]

but isn't it the hydrogen bonding that keeps the molecules close together in the first place? I mean, water in its liquid and solid states has hydrogen bonding but not in the gaseous state, so i thought that is why there is so much more energy needed to get it from liquid to gas, to break those bonds

 

[snshusat161]

yeah, you are correct. Most of the attractive force get ruptured while we get from liquid to gaseous state. Hydrogen bonding is also one among those forces.

 

[LudusRex]

The heat of vaporization is the amount of heat required to convert a liquid substance into a gas at its boiling point. In the case of water, it is approximately seven times higher than the heat of fusion, which is the amount of heat required to convert a solid substance into a liquid at its melting point. This difference can be explained by the unique properties of water, specifically its strong hydrogen bonding.

Hydrogen bonding is a type of intermolecular force that occurs between water molecules. In the liquid phase, water molecules are constantly moving and colliding with each other, breaking and reforming hydrogen bonds. This constant breaking and reforming of hydrogen bonds requires a significant amount of energy, which contributes to the high heat of vaporization.

In contrast, in the solid phase, water molecules are more closely packed together and form a lattice structure. This structure limits the movement of water molecules and reduces the number of hydrogen bonds that need to be broken, resulting in a lower heat of fusion.

Additionally, the strong hydrogen bonding in water also makes it more difficult for water molecules to escape into the gas phase, requiring even more energy to overcome these intermolecular forces and convert into a gas.

Overall, the high heat of vaporization for water is a result of its unique properties, specifically its strong hydrogen bonding, which requires a significant amount of energy to overcome in order to convert from a liquid to a gas. I hope this helps with your assignment on thermal expansion and contraction.