[Needaask]

Why is it that having stronger intermolecular forces (IMF) would mean a greater boiling and melting point?

Reading up online what I understood is that having stronger IMF would mean that at a given temperature, the potential energy is more negative than a weaker IMF substance. So when heating it up, more energy would be required to increase the PE to the point where melting/boiling can occur.

However, I was thinking if A has stronger IMF than B, then at a given temperature their average KE is the same but the PE of A is more negative than B. So, when heating both of them, each joule of energy would distribute evenly between the KE and the PE so for A there would be a smaller temperature change than B. But it doesn't tell me why A would have a greater melting/boiling point than B. I would only understand why A would have a greater specific molar capacity and not why a greater BP.

Can someone explain this to me? Thanks

[Corribus]

Overthinking it.

To boil, you need to break intermolecular bonds.  Breaking a bond takes energy.  The stronger the bonds, the more energy it takes to break them.  So substances with stronger intermolecular bonds take more energy to boil.  A higher temperature is therefore required to provide the requisite energy to break those bonds.  Therefore more and stronger intermolecular bonds results in a higher boiling point.

[Enthalpy]

Melting points are extremely complicated and not predictable up to now. While there is conceptually a link with intermolecular forces, you can completely forget and abandon any simple relation like "the stronger, the hotter".

[Needaask]

Overthinking it.

To boil, you need to break intermolecular bonds.  Breaking a bond takes energy.  The stronger the bonds, the more energy it takes to break them.  So substances with stronger intermolecular bonds take more energy to boil.  A higher temperature is therefore required to provide the requisite energy to break those bonds.  Therefore more and stronger intermolecular bonds results in a higher boiling point.

Hi Corribus

I agree that I'm overthinking it. So for now i should just understand this with the basic explanation? Cos I'm quite curious about it but i feel like i'm lacking in knowledge to comprehend it completely.

Thanks