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Homework Help: Thermodynamics Binary Phase Diagram Problem

  1. May 12, 2013 #1
    1. The problem statement, all variables and given/known data
    Refer to the attached binary phase diagram. Substance A has a melting point of 600 °C and B has a melting point of 1200 °C. A mixture of 70 weight percent B and 30 weight percent A is held at 950 °C for a long time - long enough to reach equilibrium.
    a) Determine the weight percent that is solid and the weight percent that is liquid.
    b) Determine the percentages by weight of A and B in the solid and likewise in the liquid.
    c) Check that your answers to a) and b) when taken together are consistent with the given overall composition.

    2. Relevant equations

    See attached pictures, (easier to visualize subscripts)

    3. The attempt at a solution

    Drawing a horizontal line at 950°C, I was able to find W(l) and W(s). I also found W(o) by putting a vertical line at the 70 percent mark on the horizontal axis. From this I was able to find the weight percent, however I'm not sure if it is the weight percent solid or liquid. That is pretty much where I am stuck.
    I figured out that it is 77.67 percent solid, 22.33 percent liquid.
    Now I'm just having trouble on parts b and c.

    Attached Files:

    Last edited: May 12, 2013
  2. jcsd
  3. May 12, 2013 #2
    The percentages of A and B in the solid and in the liquid phases are at the two ends of your tie line.
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