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Author Topic: Explaining boiling points of compounds  (Read 5874 times)

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positiveion

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Explaining boiling points of compounds
« on: May 17, 2010, 05:53:08 PM »

For a question I was told to put a bunch of substances in order of increasing boiling point and then explain why.

I know what order they go in but I'm not really sure how to explain it- can someone help me out with this?

C2H6
CH3CHO
CH3COOH
C2H5OH

For the latter two its cause there is hydrogen bonding and the C2H5OH has stronger hydrogen bonds. But I'm not relaly sure how to explain the first two. The reason why I put C2H6 before CH3CHO is because there is a double bond with oxygen and though the order is correct I am unsure whether that is a sufficient/valid reason to put down on an exam paper.
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mitch.fsu

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Re: Explaining boiling points of compounds
« Reply #1 on: May 17, 2010, 06:36:53 PM »

the dipole/induced-dipole and dipole-dipole attractive forces give alcohols (of similar sizes) a higher bp than alkanes like c2h6.  therefore c2h6 should have the lowest bp.

next you would look for the ones with hydrogen bonding, since it takes a large amount of energy to break these.  therefor ch3cooh and c2h5oh will have a higher bp than ch3cho.  (in ch3cho, the last hydrogen is attached to the second carbon.. not the oxygen atom)

because more energy is needed to break the double bond in ch3cooh, it will have the highest bp

- mitch
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