So what I know now is that the H in HCl is more positive and the Cl is more negative, while the H in H2O is more positive and the O is more negative. When HCl enters water, its more positive atoms (H) interact with the more negative atoms of H2O (Oxygen), and this attraction breaks the molecules apart.

However, wouldn't this mean that the dipole-dipole intermolecular force is greater than the intramolecular force? But isn't intramolecular forces stronger than intermolecular forces?

  • $\begingroup$ I can’t really answer this because I want to back this with thermodynamic data that I can’t find, but in general your assumption is wrong; the intramolecular covalent bonds are orders of magnitude stronger than dipole dipole interactions. The dissociation of $\ce{HCl}$ in water is a reaction in which new bonds are formed. $\endgroup$
    – Jan
    Aug 26 '17 at 9:43

Yes, intramolecular forces are stronger than intermolecular force. But notice that here the amount of $\ce{H2O}$ is much greater than $\ce{HCl}$, and not 1 molecule of $\ce{H2O}$ is trying to break 1 molecule of $\ce{HCl}$. Rather every molecule of $\ce{HCl}$ gets surrounded by the molecules of $\ce{H2O}$ and so the attraction by the intermolecular force gets multiplied by far and it helps to overcome the intramolecular force of $\ce{HCl}$.

Again, another noticeable fact is between $\ce{H2O}$ and $\ce{HCl}$, not only dipole dipole attraction is present but hydrogen bonding is possible too which is another pretty strong intermolecular force compared to the others.


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