Boiling Point Comparison Question: H2S vs. HCl

[medemic]

Why does hydrogen sulfide have a higher boiling point than hydrogen chloride? This doesn't make sense to me because hydrogen chloride has a greater dipole than hydrogen sulfide doesn't it? A greater dipole, I thought, would result in stronger intermolecular forces, and, thereby, a greater boiling point? Is this an anomoly?

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[Lifeman]

H2S is bent so it has a greater dipole.

 

[medemic]

H2S is bent so it has a greater dipole.

I believe you're correct...I just don't see how H2S has a greater dipole because its bent compared to HCl which I presume is linear.

 

[Temperature101]

Why does hydrogen sulfide have a higher boiling point than hydrogen chloride? This doesn't make sense to me because hydrogen chloride has a greater dipole than hydrogen sulfide doesn't it? A greater dipole, I thought, would result in stronger intermolecular forces, and, thereby, a greater boiling point? Is this an anomoly?

Not sure if HCl dipole moment is higher than H2S since the H2S has two dipole directed in the sulfur direction which sum up to give the total dipole moment even if Chlorine is more electronegative than sulfur... Remember that H2S is a bent molecule...

 

[Temperature101]

H2S is bent so it has a greater dipole.

You beat me..

 

[medemic]

Not sure if HCl dipole moment is higher than H2S since the H2S has two dipole directed in the sulfur direction which sum up to give the total dipole moment even if Chlorine is more electronegative than sulfur... Remember that H2S is a bent molecule...

Got it. Now I see. Sulfur has two dipole moments toward it compared to one in HCl

 

[medemic]

You beat me..

Another question for you guys...so take AsH3 compared to H2Se. Which has the greater dipole? Based on the previous logic, wouldn't AsH3 have the greater dipole not H2Se since it has 3 vectors pointing towards the central atom rather than two in the case of H2Se? H2Se has a greater boiling point than AsH3. Maybe I need some work at dipole moments...

 

[Idrinkwater]

HCL is a strong acid. H2S is not a strong acid. Lets assume there are HCL(aq) and H2S(aq).

Ok, so HCL(aq) will mostly disassociate to H+ and CL- .There are 2 ions here for HCL(aq) (higher boiling point elevation) . For H2S, there is only 1 (H2S does not disassociate) (lower boiling point elevation).

Thats what I would think under testing conditions. What you guys think?

I was also thinking about vapor pressure, but doesnt really apply here.

 

[Idrinkwater]

So now I am tryna figure out how boiling point elevation (HCL will have higher than H2S) is not being considered in this case, and the only explanation I can come up with is it has something to do with vapor pressure. HCL is a strong acid that disassociates in water. H2S isnte. Ka is dependent on temperature. Can H+ and CL- molecules escape from surface and result in high vapor pressure which leads to lower boiling point?

Im not sure. This is a stretch I know.

 

[medemic]

HCL is a strong acid. H2S is not a strong acid. Lets assume there are HCL(aq) and H2S(aq).

Ok, so HCL(aq) will mostly disassociate to H+ and CL- .There are 2 ions here for HCL(aq) (higher boiling point elevation) . For H2S, there is only 1 (H2S does not disassociate) (lower boiling point elevation).

Thats what I would think under testing conditions. What you guys think?

I was also thinking about vapor pressure, but doesnt really apply here.

Wait those are intramolecular forces your talking about. Boiling points have to do with intermolecular forces. Two different interactions. May the force be with you.

 

[Idrinkwater]

Wait those are intramolecular forces your talking about. Boiling points have to do with intermolecular forces. Two different interactions. May the force be with you.

They are not intramolecular interactions.

Boiling point elevation is deltaTb = kb(i)(m) (m is molality) but this has nothing to do with this question, I was trying to figure it out.

 

[Idrinkwater]

The dipole nature of H2S confers greater intermolecular interactions between molecules of H2S than between HCL. This is the reason why H2S has a greater boiling point.