Bonding of HCL and HF: Why Higher Boiling Temp for HF?

In summary, the difference in boiling temperature between hydrogen fluoride (HF) and hydrogen chloride (HCl) can be attributed to the difference in bonding. While both molecules have polar covalent bonds, HF has stronger hydrogen bonding between molecules, which requires more thermal energy to separate them. This is similar to the difference in boiling point between water and methane, which also have similar molecular weights but different bonding forces. Additionally, the higher electronegativity of fluorine compared to chlorine contributes to the stronger intermolecular forces in HF.
  • #1
Soilwork
102
0

Homework Statement


Explain why hydrogen fluoride (HF) has a higher boiling temperature than hydrogen chloride (HCL) even though HF has a lower molecular weight.


Attempt
OK so from the looks of it I think that the bonding that bonds the H to the Cl and the H to the F is polar covalent. So why would it have the higher boiling point if it has a lower molecular weight?? I mean it must have something to do with bonding because a higher boiling point means that more thermal energy is required to separate the molecules.

Any help would be greatly appreciated.

Thanks
 
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  • #2
The same rationale can be used to explain the difference in boiling point between water (MW = 18) and methane (MW = 16). Why the big difference in these two compounds of almost identical molecular weight?

I think you were on to it when you wrote, "I mean it must have something to do with bonding...".
 
  • #3
Well I've been doing some reading and I think I might have it, but I'm not entirely sure. From the looks of it there are the intramolecular bonding forces and the intermolecular bonding forces. So the intramolecular forces are polar covalent because they are responsible for the bonding of the H to the Cl and the H to the F. However, the bonding forces between the various HCl molecules (intermolecular) are weak van der Waals forces. Then for HF we have hydrogen bonding which is stronger. Is this on the right track?
 
  • #4
Doesn't F have a way higher electronegativity than Cl, implying that the van der Waals forces of attraction would be significantly greater?
 
  • #5
Soilwork said:
Then for HF we have hydrogen bonding which is stronger. Is this on the right track?

Absolutely on the right track.
 
  • #6
ahh cool. :)

Thanks!
 
  • #7
Soilwork said:
However, the bonding forces between the various HCl molecules (intermolecular) are weak van der Waals forces.

This statement isn't quite right. There is significant hydrogen bonding in HCl.
 

1. Why does HF have a higher boiling temperature than HCl?

The boiling temperature of a compound is determined by the strength of its intermolecular forces. HF has a higher boiling temperature than HCl because it forms stronger hydrogen bonds due to the higher electronegativity of fluorine compared to chlorine. This results in a more tightly held molecule and a higher boiling temperature.

2. How does the bonding of HCl and HF affect their boiling temperatures?

The bonding between HCl and HF is primarily determined by their electronegativity difference. HF has a larger difference in electronegativity, resulting in a more polar bond and stronger intermolecular forces, leading to a higher boiling temperature compared to HCl.

3. Can other factors influence the boiling temperature of HCl and HF?

Yes, other factors such as molecular weight and shape can also affect the boiling temperature of HCl and HF. Generally, molecules with higher molecular weight have stronger intermolecular forces and therefore higher boiling temperatures. Additionally, the shape of a molecule can also play a role in determining its boiling temperature.

4. How does the boiling temperature of HCl and HF relate to their physical properties?

The boiling temperature of a compound is closely related to its physical properties, such as volatility and solubility. Higher boiling temperatures generally indicate a lower volatility and higher solubility due to stronger intermolecular forces. In the case of HCl and HF, the higher boiling temperature of HF makes it less volatile and more soluble than HCl.

5. Is the difference in boiling temperature between HCl and HF significant?

Yes, the difference in boiling temperature between HCl and HF is significant and can have important implications in various industries. For example, HF's higher boiling temperature makes it useful in industries that require high-temperature reactions, while HCl's lower boiling temperature allows for easier separation and purification processes.

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