At 85oC, the vapor pressure of pure o-xylene is 55 Torr and the vapor pressure o

Question

At 85oC, the vapor pressure of pure o-xylene is 55 Torr and the vapor pressure of pure p-xylene is 85 Torr. When liquid o-xylene is mixed with liquid p-xylene, the solution formed is ideal at all compositions.

(a) Calculate G, H, and S of mixing when liquid o-xylene and liquid p-xylene are mixed at 85oC, given that the mole fraction of p-xylene is 0.30 and the solution contains a total of 4.0 mol of material.

(b) What are the mole fractions of o-xylene and p-xylene in the vapor at equilibrium with this solution?

Explanation / Answer

Delta Gmix= nRT(XalnXa+XblnXb)= 4X8.314X358X(-0.2496-0.3611)= -7.272kJ

Delta Smix=nR(XalnXa+XblnXb)= 4X8.314X (-0.2496-0.3611)= 0.0203kJ

Delta Hmix= Delta G mix+T delta Smix= -7.722-7.271=-14.542kJ

Total pressure of solution=85X0.3+55X0.7= 64 Torr

mol fraction of o-Xylene = 55X0.7/64= 38.5/64= 0.6

mol fraction of p-Xylene= 85X0.3/64= 25.5/64= 0.3984   

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