do alkenes or alkanes have a higher boiling point?

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luana35
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#1
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do alkenes or alkanes have a higher boiling point? and why? tried searching on google but just got lengthy not understandable answers.
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alberw21
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alkanes i think have a higher boiling point because they are larger hydrocarbon molecules than alkenes, so more energy is needed to break the intermolecular forces. (i might be wrong though)
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dahlia06
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(Original post by alberw21)
alkanes i think have a higher boiling point because they are larger hydrocarbon molecules than alkenes, so more energy is needed to break the intermolecular forces. (i might be wrong though)
yh i agree
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harlz_chalamet
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(Original post by alberw21)
alkanes i think have a higher boiling point because they are larger hydrocarbon molecules than alkenes, so more energy is needed to break the intermolecular forces. (i might be wrong though)
i thought it would be alkenes because they are unsaturated and have a double bond so therefore it is stronger?
Last edited by harlz_chalamet; 2 months ago
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dahlia06
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(Original post by harlz_chalamet)
i thought it would be alkenes because they are unsaturated and have a double bond so therefore it is stronger?
but alkanes have a bigger hydrocarbon compound bc its CnH2n+2 whereas alkene is CnH2n, so it makes sense it has a higher boiling point because as someone said, more energy is needed to break the intermolecular forces so more heat is needed so higher boiling point..?
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harlz_chalamet
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(Original post by dahlia06)
but alkanes have a bigger hydrocarbon compound bc its CnH2n+2 whereas alkene is CnH2n, so it makes sense it has a higher boiling point because as someone said, more energy is needed to break the intermolecular forces so more heat is needed so higher boiling point..?
ahhh okay makes sense.
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dahlia06
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(Original post by harlz_chalamet)
ahhh okay makes sense.
i see the mix of harry styles ... and timothee chalamet??
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harlz_chalamet
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(Original post by dahlia06)
i see the mix of harry styles ... and timothee chalamet??
well, one can have two husbands at once, right?

i can see lil Peep haha
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Ira Acedia
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Since there seems to be some uncertainty in this thread, generally alkanes have a slightly higher boiling point than the alkene with the same number of carbons, assuming the same arrangement of the carbon chain.

Since this is in the A-level section (I think), I'll answer in A-level terms, though adding background knowledge since, if you don't understand what is on google, then you may be a GCSE student.


Boiling points for both alkanes and alkenes are based on the amount/strength of the Van Der Waals forces/interaction (you may have seen this as London Dispersion forces, though I think this is an American term for it). This is the weakest type of intermolecular force and comes about due to random electron movement causing one side of an atom in a molecule to have more electrons due to uneven distribution, therefore meaning it is slightly more negative. This is notated as delta negative or partially negative. Therefore, it also follows that the other side is delta positive. This is called a dipole. It is also a temporary dipole, as the electrons will continue to randomly move.

The dipole in this molecule induces/makes a dipole in a nearby molecule by attracting or repelling its electrons. The partially positive part of one dipole then attracts the partially negative part of the other dipole.

When boiling the molecules, these are the forces that are being broken -- the attraction between the dipoles of neighbouring molecules.

The strength of V.D.W forces depend on the shape of the molecule (longer, straight chain has more surface area for more interactions, so higher boiling points), as well as the number of electrons (more electrons means that it can be more partially positive or negative, and therefore a larger charge and slightly stronger).

An alkene has 2 less electrons than the respective/corresponding alkane, therefore the boiling point is slightly smaller than an alkane as there are weaker intermolecular forces which need less energy to break.
Last edited by Ira Acedia; 2 months ago
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alberw21
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(Original post by Ira Acedia)
Since there seems to be some uncertainty in this thread, generally alkanes have a slightly higher boiling point than the alkene with the same number of carbons, assuming the same arrangement of the carbon chain.

Since this is in the A-level section (I think), I'll answer in A-level terms, though adding background knowledge since, if you don't understand what is on google, then you may be a GCSE student.


Boiling points for both alkanes and alkenes are based on the amount/strength of the Van Der Waals forces/interaction (you may have seen this as London Dispersion forces, though I think this is an American term for it). This is the weakest type of intermolecular force and comes about due to random electron movement causing one side of an atom in a molecule to have more electrons due to uneven distribution, therefore meaning it is slightly more negative. This is notated as delta negative or partially negative. Therefore, it also follows that the other side is delta positive. This is called a dipole. It is also a temporary dipole, as the electrons will continue to randomly move.

The dipole in this molecule induces/makes a dipole in a nearby molecule by attracting or repelling its electrons. The partially positive part of one dipole then attracts the partially negative part of the other dipole.

When boiling the molecules, these are the forces that are being broken -- the attraction between the dipoles of neighbouring molecules.

The strength of V.D.W forces depend on the shape of the molecule (longer, straight chain has more surface area for more interactions, so higher boiling points), as well as the number of electrons (more electrons means that it can be more partially positive or negative, and therefore a larger charge and slightly stronger).

An alkene has 2 less electrons than the respective/corresponding alkane, therefore the boiling point is slightly smaller than an alkane as there are weaker intermolecular forces which need less energy to break.
mate no one cares just answer the question
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Pigster
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(Original post by Ira Acedia)
...Van Der Waals forces/interaction (you may have seen this as London Dispersion forces, though I think this is an American term for it)...
The term "Van der Waals forces" was used by (at least) OCR and AQA up until a few years ago as another name for London Forces aka instantaneous dipole induced dipole forces.

BUT Van der Waals forces turn out to be the name for not only idid but also permanent dipole dipole forces. So OCR (and possibly AQA) don't like the term VdW as it isn't specific.

For the record, alberw21 is out of order. You did answer the Q. More e- -> stronger idid -> higher BP. alkanes > alkenes (if all else is equal, e.g. branching).
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dahlia06
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(Original post by harlz_chalamet)
well, one can have two husbands at once, right?

i can see lil Peep haha
LMAOO
ofc ofc gotta have his face everywhere

(Original post by Ira Acedia)
Since there seems to be some uncertainty in this thread, generally alkanes have a slightly higher boiling point than the alkene with the same number of carbons, assuming the same arrangement of the carbon chain.

Since this is in the A-level section (I think), I'll answer in A-level terms, though adding background knowledge since, if you don't understand what is on google, then you may be a GCSE student.


Boiling points for both alkanes and alkenes are based on the amount/strength of the Van Der Waals forces/interaction (you may have seen this as London Dispersion forces, though I think this is an American term for it). This is the weakest type of intermolecular force and comes about due to random electron movement causing one side of an atom in a molecule to have more electrons due to uneven distribution, therefore meaning it is slightly more negative. This is notated as delta negative or partially negative. Therefore, it also follows that the other side is delta positive. This is called a dipole. It is also a temporary dipole, as the electrons will continue to randomly move.

The dipole in this molecule induces/makes a dipole in a nearby molecule by attracting or repelling its electrons. The partially positive part of one dipole then attracts the partially negative part of the other dipole.

When boiling the molecules, these are the forces that are being broken -- the attraction between the dipoles of neighbouring molecules.

The strength of V.D.W forces depend on the shape of the molecule (longer, straight chain has more surface area for more interactions, so higher boiling points), as well as the number of electrons (more electrons means that it can be more partially positive or negative, and therefore a larger charge and slightly stronger).

An alkene has 2 less electrons than the respective/corresponding alkane, therefore the boiling point is slightly smaller than an alkane as there are weaker intermolecular forces which need less energy to break.
nah its gcse
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luana35
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#13
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#13
thanks.
(Original post by Ira Acedia)
Since there seems to be some uncertainty in this thread, generally alkanes have a slightly higher boiling point than the alkene with the same number of carbons, assuming the same arrangement of the carbon chain.

Since this is in the A-level section (I think), I'll answer in A-level terms, though adding background knowledge since, if you don't understand what is on google, then you may be a GCSE student.


Boiling points for both alkanes and alkenes are based on the amount/strength of the Van Der Waals forces/interaction (you may have seen this as London Dispersion forces, though I think this is an American term for it). This is the weakest type of intermolecular force and comes about due to random electron movement causing one side of an atom in a molecule to have more electrons due to uneven distribution, therefore meaning it is slightly more negative. This is notated as delta negative or partially negative. Therefore, it also follows that the other side is delta positive. This is called a dipole. It is also a temporary dipole, as the electrons will continue to randomly move.

The dipole in this molecule induces/makes a dipole in a nearby molecule by attracting or repelling its electrons. The partially positive part of one dipole then attracts the partially negative part of the other dipole.

When boiling the molecules, these are the forces that are being broken -- the attraction between the dipoles of neighbouring molecules.

The strength of V.D.W forces depend on the shape of the molecule (longer, straight chain has more surface area for more interactions, so higher boiling points), as well as the number of electrons (more electrons means that it can be more partially positive or negative, and therefore a larger charge and slightly stronger).

An alkene has 2 less electrons than the respective/corresponding alkane, therefore the boiling point is slightly smaller than an alkane as there are weaker intermolecular forces which need less energy to break.
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Ira Acedia
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(Original post by Pigster)
BUT Van der Waals forces turn out to be the name for not only idid but also permanent dipole dipole forces. So OCR (and possibly AQA) don't like the term VdW as it isn't specific.
I was not aware of this, thanks for sharing.

I am currently taking AQA A-Level Chemistry - Van Der Waals is considered to be all temporary/induced and dipole-dipole interactions are considered to be permanent. AQA is fine with VDW, the specification refers to intermolecular forces as the following (copy pasted).

Forces between molecules:
• permanent dipole–dipole forces
• induced dipole–dipole (van der Waals, dispersion,
London) forces
• hydrogen bonding.

Granted, having done all publicly available new specification past papers for AS and A-level, I have never seen London/dispersion forces mentioned on a mark scheme. I have seen times when VDW (as abbreviated) is rejected but Van Der Waals is underlined (i.e. mandatory to have included). There have been times where Van Der Waals is allowed as an alternative to permanent dipole-dipole interactions, but I have always considered/found this to be in situations where it isn't expected to be aware that there are permanent dipoles, for example in obscure organic compounds.

So AQA treats all 3 as synonymous and separate to permanent dipole-dipole forces.
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Pigster
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(Original post by Ira Acedia)
Forces between molecules:
• permanent dipole–dipole forces
• induced dipole–dipole forces
• hydrogen bonding.
I'd just call them pdd and idd (but don't abbreviate) and not worry about the names LDF or VdW - idd and pdd are the ones named first on the spec. so go with those names.
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