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Help with Thermo Problem, vaporization of water into evacuated vessel

  1. Feb 7, 2013 #1
    one mole of liquid water (100 deg C, vapor pressure = 1 atm) in a container is introduced into an evacuated vessel maintained at 100 deg C and allowed to evaporated. The volume of the vessel is such that the final pressure of the gaseous water is 0.1 atm. Given the (normal) latent heat of 9,730 cal per mole at 100 deg C, and assuming the vapor is ideal, calculate q, w, delta H, delta G and delta S for this process. [/b]

    So I know that I need to find a reversible path for this problem, but I don't really know where to start.
    I started by using the latent heat to find q using the formula L = Q/m
    But other than that I have no idea where to go with this. I would very much appreciate any help on this problem.
     
  2. jcsd
  3. Feb 7, 2013 #2
    Re: Help with Thermo Problem, vaporization of water into evacuated ves

    Ask yourself the following question: Is it possible for any liquid water to be remaining in the vessel if the final temperature is 100C and the final pressure is 0.1 atm? You know you have 1 mole of water, so this should give you enough information to get the volume of the vessel. Is the volume of the vessel really needed to determine the solution to the various parts of your problem?
     
  4. Feb 7, 2013 #3
    Re: Help with Thermo Problem, vaporization of water into evacuated ves

    Yeah, I can find the final volume of the vessel by using the ideal gas law, but I'm having a problem deciding a reversible path for this process.
     
  5. Feb 7, 2013 #4

    SteamKing

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    Re: Help with Thermo Problem, vaporization of water into evacuated ves

    What if there is no reversible path? The liquid water evaporates into the evacuated vessel. Unless the latent heat of vaporization is removed from the water vapor, it is not going to condense back into a liquid. With a final pressure of 0.1 atm and a temp of 100C, I would expect that very little liquid could exist.
     
  6. Feb 7, 2013 #5
    Re: Help with Thermo Problem, vaporization of water into evacuated ves

    The initial and final states are:

    Initial: 1 mole of Liquid Water at 1 atm. and 100C

    Final: 1 mole of water vapor at 0.1 atm. and 100C

    You need to figure out how to go from the initial state to the final state reversibly - not necessarily in the vessel described in the problem.

    Consider an Intermediate State: 1 mole of water vapor at 1 atm and 100C.

    How do you go reversibly from the initial state to the intermediate state? How much reversible heat is required? What is delta H. What is delta S. What is delta G?

    How do you go reversibly from the intermediate state to the final state? How much reversible heat is required? What is delta S? What is delta G?

    chet
     
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