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Why are the normal boiling points of #HF#, and #H_2O# so high?

Answer 1

Well, let's look at some figures first...........

#"Normal boiling point of water"=100# #""^@C.#

#"Normal boiling point of HF"=19.5# #""^@C.#

Now, the volatility of each solvent reflects the degree of intermolecular force, and hydrogen bonding operates in BOTH solvents as the dominant intermolecular force. So why the discrepancy?

If you look at a text, I would be surprised if you find a definitive, and comprehensive answer (certainly you will not get one from me!). Both molecules are small, and certainly in comparison to the homologous hydrides, these boiling points are high.

As far as I know, the best reason that I can advance is that the water can form 4 intermolecular bonds per molecule while #"HF"# can only form the 2. Intermolecular bonding in water also extends in 3-dimensions, whereas it is 2-dimensional in hydrogen fluoride.

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Answer 2

Cameron Andrews

The high boiling points of HF and H₂O are attributed to strong hydrogen bonding present in both molecules. This bonding requires a significant amount of energy to break, leading to elevated boiling points.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.