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Homework Help: Annoyinlgy easy problem with thermodynamics that I can't get my head around!

  1. Feb 12, 2004 #1
    I'm just answering a thermodynamics problem of my Physics homework and I just can't get my head around it here. I'll give you the quesion here, and the reason I don't get it is because you're given the mass of the substamnce as opposed to the number of moles etc....

    The latent heat of vaporisation for water at a pressure of 1 atmosphere and at 100 degrees C is 2268 J/kg.

    Assuming that the steam behaves as an ideal gasm calculate thee volume occupied by 1g of steam under these conditions. Hence calculate the work performed by 1g as it changes from liquid to gas. Using the forst law of thermodynamics, calculate the change in the internal energy of 1g of the water when it changes to gas.

    What does it mean by the latent heat as well? We've never used that term in lectures before. Thanks for your help!
  2. jcsd
  3. Feb 12, 2004 #2

    Tom Mattson

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    To get the number of moles, you will need the molecular mass of water (you can look it up for H and O on a periodic table, and combine accordingly).

    The latent heat of vaporization is the amount of heat required to change the phase from liquid to gas. It costs that much heat to change phase, and results in no increase in temperature.

    There is a nice graphic at this website:


    In the bubble map, click on "Heat and Thermodynamics", then in the next one click on "Phase Changes".
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