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Topic: Organic Chemistry - Combustion Question  (Read 3455 times)

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Offline Anime_obsessed

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Organic Chemistry - Combustion Question
« on: October 28, 2006, 10:37:10 AM »
Hi all!....never really posted anything on forums before...but whatever onto the question! I hope someone can help :)
Okay so basically I'm in grade 11 and my chem teacher has assigned an ISP where we study organic chemistry on our own...which isn't all that bad...cause this level of organic chem is pretty easy...but there's still a few questions in the assignment that me no get... ???
Well anyway...here's one of them :D What is the relationship between the number of moles of O2 (oxygen gas...no clue how to make subscripts...-.- :P) consumed in a combustion reaction and the number of -CH2 units in an alkane? (Hope this doesn't end up being an incredibly obvious answer...I'll just feel stupid :P)
So if anyone has any ideas of what the answer could be...or what the actually answer is, your input is greatly appreciated! ^_^ (though I'd kind of like it better if you just gave me a hint...you know a nudge in the right direction. :) I enjoy figuring things out for myself...but a little help along the way is always nice!)
Thanks!!
(just realized...technically this is high school chemistry...but it's also organic chem...does it matter that it's in high school section instead of organic chem?)
« Last Edit: October 30, 2006, 10:25:09 PM by Anime_obsessed »

Offline Borek

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Re: Organic Chemistry
« Reply #1 on: October 28, 2006, 11:19:25 AM »
What are products of this combustion? Write them down and the balance reaction equation:

CH2 + O2 -> ...
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Offline Anime_obsessed

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Re: Organic Chemistry
« Reply #2 on: October 30, 2006, 09:34:53 PM »
well...I know you have to make and balance an equation...it's just once I do...I see absolutely no relationship...like okay...the combustion of:
- butane : 2C4H10 (g) + 13O2 (g) --> 8CO2 (g) + 10H2O(g)
- propane : C3H8 (g) + 5O2 (g) --> 3CO2 (g) + 4H2O(g)
- pentane: C5H12 (g) + 8O2 (g) --> 5CO2 (g) + 6H2O (g)
the number of CH2 units in butane is 4? (i think)..to 13 moles of oxygen
the number of CH2 units in propane is 1? (i think)...to 5 moles of oxygen
the number of CH2 units in pentane is 3? (i think)...to 8 moles of oxygen
or...wait maybe that's not the right moles?...gaah....i don't know anymore...tired >.<...
Maybe I'm just overcomplicating this??
« Last Edit: October 31, 2006, 02:30:52 AM by Borek »

Offline Borek

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Re: Organic Chemistry - Combustion Question
« Reply #3 on: October 31, 2006, 02:35:57 AM »
Please stop posting in red. It doesn't help.

I have asked you to balance specifically given reaction.

Information you are looking for is already present in reactions you did, although it requires further work.

First of all - for butane - 13 O2 per 8 units, not 2 (what is butane coefficient in the reaction? you need oxygen per one molecule, not 2 molecules).

Second - every alkane is (CH2)nH2 - this H2 doesn't help, as it requires some additional oxygen. That's why I asked you to balance slightly different equation.
« Last Edit: October 31, 2006, 02:57:23 AM by Borek »
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