Branched and cyclic chains are more efficient in combustion.
Because they have less van der Waals' forces so less energy needed to break the molecules.

Reply 1388

otrivine

Original post by Myda

Right, I never get these basic questions!
Why would you convert straight-chained to branched in industry?
And why would you process them to cyclic?

its to increase octane rating and to burn fuel more efficiently

Reply 1389

Bright

Original post by med123

Hi can some one go over this question for me. i got this question wrong it was 3c jan 2010 paper, i got 2830 but their answer they got -2830,

here is the link of paper http://www.ocr.org.uk/download/pp_10...n_gce_f322.pdf

and mark scheme http://www.ocr.org.uk/download/ms_10...10_gce_jan.pdf

thank you

Draw hess cycle for formation.

6C+ 6H2+3O2 at the bottom, arrows up.

Then -4080-(-1240) =-2830

Reply 1390

otrivine

Original post by Little_Cat

Thanks!

Do we need t, know this because this is the first time I've heard about it?

no probs better to know it in case you can never predict what they put :wink:

Good luck

Reply 1391

TheGuy117

Explain the importance of establishing international cooperation to promote the reduction of pollution levels and waste. (4)

Reply 1392

Poffertje

Original post by med123

more efficient combustion

Original post by Little_Cat

Branched and cyclic chains are more efficient in combustion.
Because they have less van der Waals' forces so less energy needed to break the molecules.

Original post by otrivine

its to increase octane rating and to burn fuel more efficiently

Ahh right! Thanks a lot everyone! :biggrin:

Reply 1393

Little_Cat

Original post by otrivine

no probs better to know it in case you can never predict what they put :wink:

Good luck

I've learnt it right now just in case. I swear the quicker this exam is over the better it is. Last night I had a dream about radical substitution :s-smilie:

Good Luck! :smile:

Reply 1394

Little_Cat

Original post by TheGuy117

Explain the importance of establishing international cooperation to promote the reduction of pollution levels and waste. (4)

Cooperation leads to scientist sharing ideas.
All countries contribute to pollution
One country cannot reduce pollution until all countries do as well
Pollution can go over borders of other countries eg travelling in water

Reply 1395

med123

Original post by Bright

Draw hess cycle for formation.

6C+ 6H2+3O2 at the bottom, arrows up.

Then -4080-(-1240) =-2830

Thank you, i thought you had to use enthalpy change of combustion because it said work that out, so i did reactants - products.
Also it said use the enthalphy standard enathlpy changes of formation, so i would to products - reactants

Reply 1396

med123

quick questions:

Define enthalphy change of reaction?
Define bond enthalphy?

Reply 1397

otrivine

can someone send me the jan 2012 mark scheme please in which page is it?

Reply 1398

Ketchup'n'Mustard

For Jan 12 paper Q 6aii, they have asked for the formula of ion with m/z value 31 and the answer is CH3O+ or CH2OH+. How can it be those two? That would mean you have one less H atom and free unbonded electrons?

Is it because the molecule has lost an electron therefore it must have lost the whole hydrogen atom including the proton giving m/z 31?

Reply 1399

adilh301

Original post by Myda

Do we have to know this? I mean I glanced in the spec and didn't find anything on knowing anout CO2 or maybe I missed it?
Anyways in foam, they replaced CFC's. Used for decaffeinated coffee, and for dry cleaning!

I hope not it was in the book so i learnt it but that cofee stuff was real annoying so itd b best if it had no chance of coming up :smile:

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