Chemistry Help?

Hey guys, i'm a bit confused on this question,

C) there is a list of Alkanes below. For each one, say whether you think:
A: It could be used unchanged in petrol
B: It should go through a reforming process before blending to form petrol
C: It should be cracked before blending to form petrol

i) CH3CH2CH2CH2CH2CH3
ii) CH3(CH2)15CH3
iii) (CH3)CCH(CH3)CH3
iv) CH3CH2CH2CH3

Rep points for good answers! :biggrin:

(if anybody cares :tongue:

)

Reply 1

username878045

17

Well, straight chain alkanes are worse for fuels because they are less likely to undergo complete combustion, so your simple chain molecules might need to be 'reformed' to be used in petrol. Secondly, long chain alkanes are not useful because they are either too thick/viscous or are not volatile enough to ignite easily. These long chains need to be cracked to produce shorter, more useful, alkanes. So, you're looking for alkanes which have maybe 6-8 carbons in a branched chain. You can work out the individual molecules yourself, hopefully.

Reply 2

cheetahs56

OP

So i) and iv) would be fine unchanged, but the other 2 would need reforming? :s-smilie:

Reply 3

tamimi

16

Original post by cheetahs56

Hey guys, i'm a bit confused on this question,

C) there is a list of Alkanes below. For each one, say whether you think:
A: It could be used unchanged in petrol
B: It should go through a reforming process before blending to form petrol
C: It should be cracked before blending to form petrol

i) CH3CH2CH2CH2CH2CH3
ii) CH3(CH2)15CH3
iii) (CH3)CCH(CH3)CH3
iv) CH3CH2CH2CH3

Rep points for good answers! :biggrin:

(if anybody cares :tongue:

)

i)
a: Super bad for fuel cus it's a long chain with no branches so it has a silly Octane value and won't completely combust.
b: Definitely needs to be reformed first for the reason mentioned earlier.
c: Sure, why not, it's long enough to be crached.

ii)
a: Worst. cus of super long chain.
b: Sure, reform it. I don't see why not.
c: Oh yes, crack it multiple times.

iii)
a: Pretty decent for fuel.
b: Doesn't need reforming really.
c: No need to crack it either.

iv)
a: It's probably 2nd best for fuel out of the lot, because although it's a short chain, it's very uniform.
b: as it's uniform, reforming it is a big yes.
c: no need for cracking as chain is tiny.

Reply 4

cheetahs56

OP

Original post by tamimi

i)
a: Super bad for fuel cus it's a long chain with no branches so it has a silly Octane value and won't completely combust.
b: Definitely needs to be reformed first for the reason mentioned earlier.
c: Sure, why not, it's long enough to be crached.

ii)
a: Worst. cus of super long chain.
b: Sure, reform it. I don't see why not.
c: Oh yes, crack it multiple times.

iii)
a: Pretty decent for fuel.
b: Doesn't need reforming really.
c: No need to crack it either.

iv)
a: It's probably 2nd best for fuel out of the lot, because although it's a short chain, it's very uniform.
b: as it's uniform, reforming it is a big yes.
c: no need for cracking as chain is tiny.