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How to calculate change in pressure from LN2 phase change

  1. Aug 7, 2018 #1
    I am trying to calculate the increase in pressure caused by liquid nitrogen when it changes from liquid to vapor within a closed, constant volume at atmospheric pressure. How can this be done? Do I need to include the heat of vaporization?
     
  2. jcsd
  3. Aug 8, 2018 #2

    Tom.G

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  4. Aug 8, 2018 #3
    So, the vapor pressure is an accurate representation of the pressure exerted by the LN2 gas on the walls of any closed container?
     
  5. Aug 8, 2018 #4

    Tom.G

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  6. Aug 8, 2018 #5
    I don't agree: "defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid)" but maybe i am missing something. To clarify, I am looking for the pressure exerted on the walls of the container.
     
    Last edited: Aug 8, 2018
  7. Aug 8, 2018 #6

    Bystander

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    Zero is identically "zρ." Now, what is your question? Did you want vapor pressure as a function of temperature?
     
  8. Aug 12, 2018 at 12:54 AM #7
    Let's say you start with a mol of LN2 at one atmosphere at its boiling temperature, and you fix a cap on it (constant volume). You can look up the volume it displaces and the temperature on your own...

    Add heat until it's all evaporated. As it evaporates, pressure rises, and boiling temperature rises. You know you have a molar volume of vapor (starting with one mol N2), so look up the temperature/pressure of N2 gas with that molar volume in equilibrium with liquid. If you run out of table before you get to that volume, then you can probably stop at the critical temperature, and find the (supercritical) pressure that provides the correct molar volume.
     
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