Why is the normal boiling point of #HF# (#19.5# #""^@C#), so high compared to that of #HCl# (#-85.0# #""^@C#)?

Answer 1

For the same reason that water is a liquid at room temperature and pressure, whereas #H_2S#, #H_2Se#, and #H_2Te# are gases.

So the simple reason underlying these phenomena is hydrogen bonding. Fluorine is a smaller, more polarizing atom than chlorine. Charge separation in the #H-F# molecule should be greater, and the bond strength of #H-X# should thus be greater when #X=F#. Of course, this principle manifests in the acid strength of #HCl# versus #HF#. #HF# is a poor acid in water.
Because there is greater polarity in the #H-F# bond, the opportunity for hydrogen bonding in the bulk solvent is greater. The best metric for this INTERMOLECULAR force is the boiling point. #HF# has a normal boiling point of #19.5# #""^@C#, whereas that of #HCl# is #-85.0# #""^@C#. Also compare the boiling points of water versus #H_2S#, and #H_2Se#.
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Answer 2

The higher normal boiling point of HF compared to HCl is due to the stronger hydrogen bonding present in HF molecules, which requires more energy to break compared to the weaker dipole-dipole interactions in HCl molecules.

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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.

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.

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.

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.

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