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Homework Help: Find the change in enthalpy

  1. Feb 6, 2012 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    [itex]h_2 - h_1 = (u_2 + P_2v_2) - (u_1 + P_1v_1)[/itex]

    3. The attempt at a solution

    I thought I had to look at the charts in the book for saturated liquid, then notice that the temperature is much higher at the given pressure than what was given in the problem. That would tell me for both situations I have a compressed liquid. But the thing is when our pressure isn't listed in the compressed liquid tables, we are supposed to look at the saturated liquid tables under the given temperature to determine an equivalent amount for what we are trying to solve. In this case it would be enthalpy. And this is true for both cases, which would make the enthalpy zero overall as there is no change in enthalpy between constant temperatures. So I must be approaching this wrong. What is another method to solve this problem?
  2. jcsd
  3. Feb 7, 2012 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    ΔH = ΔU + Δ(PV) = ΔU + VΔP + PΔV

    Since ΔV = 0 (it is negligible) this is simply: ΔH = ΔU + VΔP

    What is ΔU here? What is VΔP?

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