Questions about alkenes/ alkanes- please answer!

Watch
vix.xvi
Badges: 13
Rep:
?
#1
Report Thread starter 6 months ago
#1
I have a few questions about alkene/alkanes for GCSE chem. I'd appreciate any help with any of the questions. Thanks in advance!

1- why are alkanes used as a fuel and not alkenes
2- Why are alkenes not found in crude oil? And why must they be obtained by cracking?
3- Why are alkenes used to make plastic bags?
Last edited by vix.xvi; 6 months ago
0
reply
Mr Wednesday
Badges: 18
Rep:
?
#2
Report 6 months ago
#2
(Original post by vix.xvi)
I have a few questions about alkene/alkanes for GCSE chem. I'd appreciate any help with any of the questions. Thanks in advance!

1- why are alkanes used as a fuel and not alkenes
2- Why are alkenes not found in crude oil? And why must they be obtained by cracking?
3- Why are alkenes used to make plastic bags?
Try answering (2) first, that gives you an interesting way of starting to answer (1). Hint, oil in the ground has been there for a long time so if there is the possibility of a reaction happening, it is likely to have done so.

For (3) how does polymerisation work and what kind of molecule would make a good starting point ? What kind of polymer are plastic bags often made of ? Hint, to make a polymer your starting point must have something that can be used to attach to another molecule. That might be a functional group, or a double bond that can be opened up and attached somewhere else.
Last edited by Mr Wednesday; 6 months ago
0
reply
vix.xvi
Badges: 13
Rep:
?
#3
Report Thread starter 6 months ago
#3
(Original post by Mr Wednesday)
Try answering (2) first, that gives you an interesting way of starting to answer (1). Hint, oil in the ground has been there for a long time so if there is the possibility of a reaction happening, it is likely to have done so.

For (3) how does polymerisation work and what kind of molecule would make a good starting point ? What kind of polymer are plastic bags often made of ? Hint, to make a polymer your starting point must have something that can be used to attach to another molecule. That might be a functional group, or a double bond that can be opened up and attached somewhere else.
Thanks for replying!! I understood Q3, but do you mind going through one and two again, please? Tysm!
0
reply
Mr Wednesday
Badges: 18
Rep:
?
#4
Report 6 months ago
#4
(Original post by vix.xvi)
Thanks for replying!! I understood Q3, but do you mind going through one and two again, please? Tysm!
Ok, a few more hints. If you want to burn a fuel, would it be sensible to use something that requires more or less energy input / processing to get it into a usable form ?

Re (2) "Why are alkenes not found in crude oil ?" .... Thats a bit of a fudge (as is often the case in GCSE to keep the level of complexity managable).

You do find some alkenes with C=C bonds in crude oil, just not very much compared to alkanes and stable rather structures like benzene rings. Why not .... alkenes are more reactive than alkanes with just C-C bonds and that C=C double bond can be opened up more easily to attach to something else. If you cook crude oil under pressure and relatively high temperature for a few million years, odds are many of the C=C bonds will find something to react with, so not many survive to be refined out of the crude.
Last edited by Mr Wednesday; 6 months ago
1
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

Regarding Ofqual's most recent update, do you think you will be given a fair grade this summer?

Yes (129)
29.86%
No (303)
70.14%

Watched Threads

View All