Combustion Q (only read if you've taken AAMC 9)

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Eye Cue

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I take the MCAT on Tuesday, and I have a last minute question.

If both compounds undergo complete combustion, 1 mole of which will require the least amount of oxygen?

Propanol (H3C-CH2-CH2-OH) or Glucose (C6H12O6)?

*There was a similar question to this on AAMC 9, which I got correct, but under a different logic. According to AAMC, the compound with the lowest carbon-to-oxygen ratio will undergo combustion more easily, which in this case would be glucose (1:1 ratio as opposed to propanol's 3:1 ratio). However, glucose is much bigger, so my instinct is telling me that it would require more oxygen. Also:

C3H8O + 4.5O2 --> 4H20 + 3CO2
C6H12O6 + 6O2 --> 6H20 + 6CO2

I'm sure there are probably other factors involved to go along with AAMC's explanation, but could someone please clarify? Thanks.

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As you can see, I clarified as far as I could.

According to my knowledge, it is as simple as making a balanced equation, but AAMC stated that it is all about the carbon-to-oxygen ratio. But above, I stated an example in which it seems as though the AAMC explanation of the carbon-to-oxygen ratio does not apply.

So for a question as the one I asked, I am curious... do we stick with the obvious 'balanced-equation' method or would we go with AAMC's 'ratio' method?

(I hope I am doing an okay job at getting my point across, lol)
 
First look at the number of carbons... when you balance combustions u equalize the CO2 to the alkane. and Co2 contributes a lot of the needed oxygen.

So, the more oxygens in the alkane WOULD help, since it means less O2 is needed on the left. However, the main contributor is those Carbons on the alkane that require Co2 be made. I think they're rule only applies when you're comparing two things that have almost the same number of carbons. At which point the one with more oxygens in the alkane will need less O2's on the left.
 
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First look at the number of carbons... when you balance combustions u equalize the CO2 to the alkane. and Co2 contributes a lot of the needed oxygen.

So, the more oxygens in the alkane WOULD help, since it means less O2 is needed on the left. However, the main contributor is those Carbons on the alkane that require Co2 be made. I think they're rule only applies when you're comparing two things that have almost the same number of carbons. At which point the one with more oxygens in the alkane will need less O2's on the left.


should be rule applies when you have a similar number of oxygens... not carbons right?
 
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