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Helmholtz energy problem

  1. Apr 11, 2009 #1
    1. The problem statement, all variables and given/known data

    Explain why the formula (dF/dV)=-P , where T and N are constant variables , makes intuitive sense, by discussing graphs of F vs. V with different slopes.

    2. Relevant equations



    3. The attempt at a solution

    dF=SdT-PdV+mu*dN

    dT and DN are zero since T and N are fixed.

    As volume increases, P will be negative. as dV increase and P remains negative, then I suspect F will decrease therefore the slope dF/dV will be a negative value.
     
  2. jcsd
  3. Apr 11, 2009 #2

    Mapes

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    This is a good start. So what would it mean if a graph of F vs. V had a very large or very small negative slope for a particular material?
     
  4. Apr 11, 2009 #3
    If dF/dV had a very small slope, would the slope be closed to the shape of that of a vertical line and the change in dV would be very small?
     
  5. Apr 11, 2009 #4

    Mapes

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    A small slope means that the line is nearly horizontal.
     
  6. Apr 11, 2009 #5
    oh yeah, since the slope of a horizontal line is zero. that means dV is approaching inifinty.
     
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