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Homework Help: Thermodynamics - Using steam tables to find unknowns

  1. Apr 7, 2010 #1
    1. The problem statement, all variables and given/known data
    Determine the temperature, quality, and internal energy of 5 kg of (pure) water in a rigid container of volume 1 m3 at a pressure of 2 bar.

    2. Relevant equations
    PV = nRT (maybe?)
    quality = nv/(nl + nv) where l = number of moles in liquid phase and v = number of moles in vapor phase

    3. The attempt at a solution
    So far I have been able to determine that since P = 2 bars, it is also equal to 200 kPa.
    V is also equal to 1000L.
    5kg H2O*(1000g/1kg)*(1 mol H2O/18.01g H2O)=277.53 moles H2O.
    Plugging this into the ideal gas equation, and rearranging to solve for T, I got this:
    T = (200 kPa)(1000L)/(277.53 moles)(8.314 J*mol-1*K-1) = 86.68K = -186.47oC

    First off, are my calculations correct? If not, where did I go wrong?
    Secondly, once temperature is correctly solved for, how do I use that information with steam tables to find out the internal energy and composition of water in the liquid and vapor phases? My textbook does not give any examples of how to calculate those.
  2. jcsd
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