Determining Higher Boiling Points

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Jane Burgan 1C
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Joined: Fri Sep 28, 2018 12:15 am

Determining Higher Boiling Points

Postby Jane Burgan 1C » Sat Nov 24, 2018 10:57 am

Predict which would have a higher boiling point: HBr or HI.
I thought HBr has higher boiling point compared to HI, because Br is smaller than I, meaning that the bond length between H and Br is shorter and stronger, so it would be harder to break this bond. But, the answer is HI. Can someone explain why?

Mariam Baghdasaryan 4F
Posts: 37
Joined: Fri Sep 28, 2018 12:29 am

Re: Determining Higher Boiling Points

Postby Mariam Baghdasaryan 4F » Sat Nov 24, 2018 1:08 pm

It is true that the H-Br bond length is shorter than the H-I bond length. However, what you need to consider is also the size of the atoms. I is a larger atom than Br, so it has more electrons that increase the strength of the dispersion forces and the attractive interactions. Due to the greater attraction, more energy is needed to break the bonds.

Christopher Wendland 4F
Posts: 30
Joined: Fri Sep 28, 2018 12:29 am

Re: Determining Higher Boiling Points

Postby Christopher Wendland 4F » Sat Nov 24, 2018 1:26 pm

The bond between H and Br might be stronger than the bond between H and I; however, that is not what matters in boiling point, the strength of the intermolecular bonds is what matters. I has more electrons and therefore stronger dispersion forces than HBr so it has stronger bonds between its individual molecules and therefore it is harder to break those intermolecular bonds.


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