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Evaporation and condensation problem

  1. Feb 20, 2009 #1
    Hi,

    I'm now studying evaporation and condensation and I have a question.

    Why even when water boils, its temperature doesn't exceed 100 C?
    Where did the energy gotten from environment go? What was it used for?

    Examining structure of water and vapour molecules are given as a hint, but I see no correlation between that energy case and structure of molecules.

    Are there some rules concerning kinetic energy of a liquid?




    Also - I think it's related - why people feel cold after warm bath?
    Is it because our body gives heat to environment?
     
    Last edited: Feb 20, 2009
  2. jcsd
  3. Feb 20, 2009 #2

    LowlyPion

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    Homework Helper

  4. Feb 20, 2009 #3
    Re: Evaporation

    This is a tricky one to explain without giving it totally away.

    If ive got the gist of the question right: What happens when you get some water to 100 c, does it all instantly turn to steam? What happens to the liquid?

    hint: imagine a pan of boiling water without a lid left on the cooker.

    What level are you studying at? And you are perfectly correct about the molecules they are both H2O and that is an awful hint.

    :P Damn Pion gave the game away.
     
  5. Feb 20, 2009 #4
    Re: Evaporation

    Oh yes, Pion, thank you. I understand it now.

    However, I still don't know the answer to the second question and I will probably get it on the test, so I'd be grateful if someone explained.
    I thought it must have something to do with giving or getting heat, am I right?
     
  6. Feb 20, 2009 #5

    LowlyPion

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    Re: Evaporation

    If you mean arising from a tub of warm water and feel the chill, then what you are feeling is evaporation. But what is evaporation? The escape of more energetic water molecules to the atmosphere?
     
  7. Feb 20, 2009 #6
    Re: Evaporation

    You are correct about heat, so long are you are not comfusing it with temperature :P

    Back to the pan example: although the temperature stays at 100 c you are still putting in energy (heat) to change the 100 c liquid water to 100 c water vapour.

    http://www.spiraxsarco.com/images/resources/steam-engineering-tutorials/2/2/fig_2_2_3.gif

    (cant be bothered linking it) hooray for auto links!!

    if you look at this you can see that from A to B the temp rises. From B to C you are still adding energy but the temperature is the same as liquid ------> steam and from C onwards heat is still being added and the steam increases in temp.
     
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