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(a) Tabulate the activity coefficient of A as a function of composition.

(b) Over what range of composition is Henry's law obeyed by A?

(c) What is the equation for the equilibrium partial pressure of B in the composition range in which component A obeys Henry's law?

8.11 Shown below are the free energy Vs composition plots for an A-B binary ststem at four temperatures. The ordinate is the free energy and the abscissa is the mole fraction of component B.

Increasing temperature —>

Increasing temperature —>

(a) On these plots, label the melting temperatures of the pure components. Draw common tangent lines on the plots and indicate with letters the points of common tangency on the solid and liquid curves.

(b) From the identifications made in part (a), sketch the phase diagram derived from the free energy plots.

8.12 The silver-praseodymium phase diagram is shown below

(a) Identify the 12 numbered regions.

(b) What is the partial pressure of silver in equilibrium with the liquid at point P on the diagram? The vapor pressure of pure solid silver at 900oC is 4 x 10-8 atm and its heat of fusion is 2.7 kJ/mole. The enthalpy of sublimation is 89 kJ/mole.

Hint: Note the similarity to Fig. 8.11. You must calculate the vapor pressure of pure liquid silver at 900oC in order to use Eq (8.5).

(c) Assuming regular solution theory to apply, what is the partial pressure of silver in equilibrium with the liquid at point Q?

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8.13 Identify the phases present in the numbered areas of the following phase diagram:

8.14 The A-B phase diagram shown below is typical of two substances that show partial miscibility in the solid state. Identify the numbered phases, the point P and the curve RS.

8.15 The Pb-Sn system exhibits regular-solution behavior with an interaction energy

(a) If the ratio of the vapor pressure of pure lead to that of pure tin at 200oC is 2.5, what is the ratio of the partial pressures of lead and tin at the same temperature in equilibrium with a solution containing 60 mole percent lead?

(b) At what temperature does the solution separate into two immiscible phases?

(c) What is the activity coefficient of lead in a solution with xPb = 0.3 at 500oC?

8.16 Consider a mixture of A and B with 50 mole percent B whose temperature is increased from room temperature. The phase diagram of this system is shown on the following page.

(a) What is the composition of the liquid phase that first forms?

(b) At 70oC what is the mole ratio of solid to liquid?

(c) What are the activity coefficients of A and B in the liquid and solid phases at 80oC? Assume regular solution behavior with AHma = 10 kJ/mole and 12 AHMB = 10 kJ/mole

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