Why do alkenes have lower MPs and BPs? (1 Viewer)

[aim54x]

threads get too long n ppl will repeat stuff. sori i didn't read ur stuff first.
clarification is a good thing

 

[Slidey]

that looks just fine (I tend to say put inter- or intra- before molecular though, molecular is kinda obscure to me, I actually had to read it three times but I guess it does imply intramolecular) ^_________^ hey slidy, what did you mean by when you actually knew some chemistry? I remember you used to have some amazing Chem things to say last year.. so you should know more Chemisty now? not less?

Thanks. Good point.

Lack of confidence, I guess. I'll build it up eventually. It doesn't help that while most people were doing Acids, I was doing Shipwrecks.

But also I think we have a lot of good chem students (HSC and uni) on these forums, so I tend to come too late even when I can help out.

 

[mitochondria]

umm.. I'm studying hard to keep up with Chem and I'll be staying for quite a while.. or so it seems ^_________^ anyways.. you neeeeed confidence go on, yell "HSC occidebis!" a few times and you'll be fine it feels like you're going to do great anyway

 

[xiao1985]

ok did we reach a common conclusion abt why saturated hydrocarbons have higher bp/mp as comparing to unsaturated?!

i think i got a pt there... tho ... =S

 

[nit]

It's just a combination of the two major ideas in this thread- alkenes have lower BP/Mp than alkanes because a.) there are less atoms present in the non-polar alkene as opposed to alkane leading to lower van der waals' interactions, and b.) the rigidity of the double bond entails that the activation energy for double-bond rotation is much greater than that for the flexible, weak, longer C-C bond, meaning that in general, alkenes will tend to have kinks in them (think fatty acid chains for example). This in turn means that there will be less overlap of alkene molecules vs alkanes which leads, once more, to lower van der waals' forces between alkenes and alkanes.

 

[xiao1985]

hm flexibility in single bond... i missed that... =p
u go nit ^^

btw, how's maths goin?! =p

 

[nit]

maths is going fine atm, xiao - I have a feeling it's going to take off soon with matrices and the linear algebra course starts next week I think. We have a 1902 quiz week after next but it's only on vectors so it won't be too difficult I think.