why do branched chains have lower boiling points?

Watch
Narsha
Badges: 11
Rep:
?
#1
Report Thread starter 14 years ago
#1
hi, the text book says that alkanes with branched chains have lower boiling points thn the straight carbon chain with the same number of carbon atoms. but it doesn't explain. does anyone know why?
0
reply
3.14159265
Badges: 13
Rep:
?
#2
Report 14 years ago
#2
branched alkanes have weaker van der waals forces because of the smaller area of contact between the molecules.

so less energy is needed to overcome the intermolecular force.

Linear alkanes can line up more closer and therefore have stronger van der waals forces than unbranched alkanes.

so just remember that van der waals forces are stronger when there is more area of contact between molecules, and obviously area of contact is smaller in branched molecules compared to linear molecules (when they both have the same molecular formula).
4
reply
charco
Badges: 17
Rep:
?
#3
Report 14 years ago
#3
Just to add that a sphere is the shape with the smallest surface area to volume ratio. The more branching there is the more spherical is the molecule and hence the smaller surface area for a given volume (relative molecular mass).
2
reply
Magnamind
Badges: 1
Rep:
?
#4
Report 1 year ago
#4
Alkanes have intermolecular forces, i.e. Van Der Waal's forces that control their boiling points. ... A straight chain alkane will have a boiling point higher than a branched chain alkane because of the greater surface area in contact with other molecules.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Have you experienced financial difficulties as a student due to Covid-19?

Yes, I have really struggled financially (44)
18.72%
I have experienced some financial difficulties (67)
28.51%
I haven't experienced any financial difficulties and things have stayed the same (88)
37.45%
I have had better financial opportunities as a result of the pandemic (30)
12.77%
I've had another experience (let us know in the thread!) (6)
2.55%

Watched Threads

View All
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise