I am currently learning about the physical properties of alcohols.

I understand that the main intermolecular forces between alcohols and water are hydrogen bonds. When these two are mixed, the intermolecular hydrogen bonds between alcohol and water are broken and hydrogen bonds between alcohol and water molecules are formed. I also read that as an alcohol's hydrocarbon chain gets longer, it is less soluble, as the hydrocarbon part is hydrophobic and that is becoming more significant (while the OH becomes less significant).

There's one part I'm confused about. I read a website which stated that:

The energy released when these new hydrogen bonds are made more or less compensates for that needed to break the original ones.

I understand what the author is trying to say here, but I'm confused about why this needs to happen? Why does the energy need to be "more or less compensated"? Why can't long alcohols just break their hydrogen bonds and form weaker van der Waals forces with the water (the hydrocarbon part cannot form hydrogen bonds).

  • $\begingroup$ Such mixing would be too endothermic for the entropy increase to cover it. $\endgroup$
    – Poutnik
    Apr 24 '19 at 10:41
  • $\begingroup$ The compensation is required as the first step is unfavourable(breaking of alcohol-alcohol H bonds). The intrusion of water into alcohol's pre-existing network of H bonds would be "compensated" by water forming new H bonds with alcohol molecules. $\endgroup$ Apr 24 '19 at 10:53
  • $\begingroup$ Sorry, but what is meant by the 'intrusion' of water? $\endgroup$ Apr 24 '19 at 11:28

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