March 28, 2024, 10:11:22 PM
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Topic: I can't find enhalpies of combustion for isomers of Decanoic & Eicosanoic acids!  (Read 4120 times)

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Offline emu

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Hi! I'm new to the forum, and apologise if I'm writing in the wrong forum..

I need to prove in a statement, that the ACID isomers of the LINEAR ACIDs c10h20o2 and c20h40o2 (decanoic and eicosanoic) are different when it comes to heat/enthalpy of combustion (preferably in liquid).

I have searched and searched but just can't seem to find these numbers anywhere (meaning for the isomers, I do have them for the linear molecules) 

Could someone who knows a site where to find them, link them for me, or if you have the numbers (kJ/mol) please write them here and tell the source.

Million thanks to whoever has the answers!!! I'm in a rush with this, so the sooner the better! Thank you.


Offline Babcock_Hall

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Is this a homework assignment?  Can you tell us where you have searched?

Offline Corribus

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Well for one thing you won't find heats of combustion for liquid phase because combustion happens in the gas phase.

The data you want also may simply not exist - as molecules get larger it's often difficult to find thermodynamic data for different isomers because of the difficulty (or cost) of purifying them.

If you checked NIST database, and the CRC, and didn't find the molecules you are looking for, you may be out of luck.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline Arkcon

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I need to prove in a statement, that the ACID isomers of the LINEAR ACIDs c10h20o2 and c20h40o2 (decanoic and eicosanoic) are different when it comes to heat/enthalpy of combustion (preferably in liquid).

Also, why are you highlighting the word 'ACID', are you trying to compare the enthalpy of acid to base form?
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline sjb

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Also, why are you highlighting the word 'ACID', are you trying to compare the enthalpy of acid to base form?

As opposed to e.g. esters, or keto-alcohols I guess?

Offline Enthalpy

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Heats of formation or combustion are scarce data. They must be measured individually but there are so many compounds.

If the isomerism, like branching, is at least 2 carbons away from the acid, then you can apply to the acids the difference observed on the alkanes. Some data exists for the alkanes; the "CRC Handbook of Chemistry and Physics" is a convenient compilation. Doing this needs some caution. Whether this will be a "proof"? To my eyes, only measures in a lab would prove it.

The difference is small, especially for a combustion.

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