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Which has a higher boiling point - alkane or alkene? [PLEASE HELP / DISCUSSION]

I thought it would be alkanes as there are more electrons available due to 2 more hydrogen bonds, so the London forces would be stronger so more energy is needed to overcome these.

Any comments?

Assume the discussion concerns ethane and ethene.
I'm pretty sure I haven't seen such a question before simply because they are both very similar. The 2 extra hydrogen atoms don't do much to help vdw forces because H atoms only have 1 electron each. 2 electrons overall make little to no difference. Therefore, the difference in boiling points would be negligible.
Original post by nwmyname
I thought it would be alkanes as there are more electrons available due to 2 more hydrogen bonds, so the London forces would be stronger so more energy is needed to overcome these.

Any comments?

Assume the discussion concerns ethane and ethene.
I think it's the alkene because it has a double bond so more energy is required to break the pie/ sigma bond?
Reply 3
Avatar for alow
alow
19
Original post by RedRosesBloom
I think it's the alkene because it has a double bond so more energy is required to break the pie/ sigma bond?


How does a boiling point have anything to do with covalent bonds? And it's pi, or π. Not pie.
Original post by alow
How does a boiling point have anything to do with covalent bonds? And it's pi, or π. Not pie.
Ok Mr. Sherlock. I said 'i think' not 'this is the right answer'.
Reply 5
Avatar for nwmyname
nwmyname
OP
13
Original post by rosemondtan
I'm pretty sure I haven't seen such a question before simply because they are both very similar. The 2 extra hydrogen atoms don't do much to help vdw forces because H atoms only have 1 electron each. 2 electrons overall make little to no difference. Therefore, the difference in boiling points would be negligible.


Yes I mean they would be negligible but on smaller margins, the alkane would still have the higher boiling point, right?
Original post by alow
How does a boiling point have anything to do with covalent bonds? And it's pi, or π. Not pie.


the enthalpy change in breaking a double bond would be greater than in a single bond
Original post by RedRosesBloom
Ok Mr. Sherlock. I said 'i think' not 'this is the right answer'.


yeah but it doesn't take a genius to work out that covalent bonds aren't broken when a compound is boiled
Original post by richpanda
yeah but it doesn't take a genius to work out that covalent bonds aren't broken when a compound is boiled
Yes, I know. Calm down genius, I didn't say it did!
(edited 7 years ago)
Original post by RedRosesBloom
Yes, I know. Calm down genius, I didn't say it did!
not...sure...if...serious. You are aware that a pi and sigma bonds are covalent bonds?
Original post by RedRosesBloom
I think it's the alkene because it has a double bond so more energy is required to break the pie/ sigma bond?
Original post by richpanda
not...sure...if...serious. You are aware that a pi and sigma bonds are covalent bonds?
YES I'm aware. I meant that I didn't say, it takes a genius to work out that covalent bonds aren't broken when a compound is boiled
The boiling points are very similar but alkenes in general (for the same length of chain) have a boiling point a small number of degrees lower than the corresponding alkane.

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