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Boiling and distance traveled

  1. Dec 23, 2015 #1

    faiziqb12

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    i have got a question with distillation . in distillation as we know the mixture is boiled and the mechanism then goes like substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top.
    i dont know why , but i am having difficulty understanding that why should a substance with high boiling point go to the bottom and the substance with the low melting point get higher . it is going against my intuition .
    basically what i think is that higher boiling point means greater energy to the system and thus higher output in form of reaching higher . now according to the real observation i am wrong.

    so does the system behave like this .
    higher boiling point means that after the system changes into gaseous state (most probably) , it radiates energy more fastly that the substance with the lower melting point .

    Is this explanation of the phenomena correct

    if yes
    then explain why does the substance with more boiling point radiate energy more fastly ?

    if no
    then please correct me with the right mechanism
     
  2. jcsd
  3. Dec 23, 2015 #2

    Bystander

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    No. No. No.
     
  4. Dec 23, 2015 #3

    faiziqb12

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    kindly please , give the right mechanism then
    its confusing me a lot
     
  5. Dec 23, 2015 #4

    faiziqb12

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    Sir ,
    is it that more energy gets absorbed by the liquid with the lesser boiling point , then
     
  6. Dec 23, 2015 #5

    Bystander

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    What DO you know? This isn't even close to being a misunderstood/garbled question. I need some place to apply a little leverage.
     
  7. Dec 23, 2015 #6

    faiziqb12

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    i am sorry for being so dull , but i cant imagine the situation .the lower boiling point rising to a higher level seems like the lower boiling point gets more energy. is it that the lower boiling points get energy even after changing into liquid
    true sir ?
     
  8. Dec 23, 2015 #7

    jbriggs444

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    Have you ever encountered the terms "vapor pressure", "partial pressure" or "saturated vapor pressure"?
     
  9. Dec 23, 2015 #8

    SteamKing

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    You're getting mixed up by your intuition here.

    Let's say you take a mixture of ethanol and water at an initial temperature of 20° C. Both substances are liquid at this temperature and let's specify that the ambient pressure is 1 atmosphere, to keep things friendly.

    The boiling point of ethanol is about 78° C while water has that well-known boiling point of 100° C at the ambient pressure.

    What happens to the mixture of ethanol and water as it's heated and the temperature starts to rise above 20°?

    The temperature of the mixture is going to reach 78° eventually, and what happens to the ethanol? At 78°, what is the water doing?

    This process is what is known as fractional distillation, and it's used not only in making potable spirits, but it's also used quite extensively in refining petroleum:

    https://en.wikipedia.org/wiki/Fractional_distillation

    All that stuff about substances radiating energy 'more fastly' has nothing to do with this process.
     
  10. Dec 23, 2015 #9

    Dale

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    Which is a higher temperature, the top or the bottom of the column?
     
  11. Dec 23, 2015 #10

    faiziqb12

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    both are the same because the column is a homogenous system
     
  12. Dec 23, 2015 #11

    jbriggs444

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    Did you read the link that SteamKing provided?
     
  13. Dec 23, 2015 #12

    Dale

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    No, that is not correct at all. The temperature gradient along the column is crucial for the function of the still.
     
  14. Dec 23, 2015 #13

    faiziqb12

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    that explains it hopefully
    but how are gases distilled in the fractional distillation column with marbles present ?
    does it also have have a trempreature gradient?
     
  15. Dec 23, 2015 #14

    SteamKing

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    It's not clear where you are getting marbles from.

    If you look at the diagram of the crude oil separator column in the Wiki article, you'll see that temperatures range from 400° C at the bottom to 150° at the top.
     
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