Thermodynamics - Questions from Phase Equilibria

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  1. What is the significance of Van Laar constants? The vapor pressure of carbon tetra chloride - ethanol solutions are given below at 34.8oC.
  2. Weight percent CCl4 Vapor pressure, mm Hg
    0100
    10.23 103
    20 142
    27.13 156
    39.06 179
    43.87 187
    48.86 193
    58.25 206
    71.68 220
    76.69 222
    84.25 226
    92.98 225
    97.43 221
    98.46 213
    100203

    Calculate the Van Laar constants for this system at 34.8oC.

  3. Using Van Laar method, compute the x-y curve for ethanol-water mixtures at a total pressure of 760 mm Hg. Base the computations on the composition of the azeotrope 89.43 mole % alcohol at 78.15oC. Vapor pressures at 78.15oC: ethanol = 755 mm Hg; water = 329 mm Hg.
  4. From the following vapor pressure data, construct the temperature - composition diagram at 1 atm, for the system benzene-toluene, assuming ideal solution bahaviour.
  5. Temperature oC

    Vapor pressure, mm Hg

    Benzene Toluene
    80 760 300
    92 1078 432
    100 1344 559
    110.4 1748 760
  6. Construct Pxy diagram for the cyclohexane(1) - benzene(2) system at 40oC. Use the following expressions for the liquid-phase activity coefficients:
  7. ln g 1 = 0.458 x22

    ln g 2 = 0.458 x12

    At 40oC, P1sat = 0.243 atm; and P2sat = 0.241 atm.

  8. The vapor pressure of components A and B of a binary system at 80oC and 760 mm Hg are 540 mm Hg and 620 mm Hg respectively. An azeotrope contains 20% A at 80oC. Find Van Laar constants. What is the composition of a vapor corresponding to a liquid composition of 80% A?
  9. The azeotrope of propanol-water system has a composition of 43.2 mole % of propanol with a boiling point of 87.8oC at a total pressure of 760 mm Hg. The vapor pressures of propanol and water at this temperature are 524 and 483 mm Hg respectively. Calculate the Van Laar constants and evaluate the activity coefficients of propanol and water for a solution containing 30 mole % propanol.
  10. The vapor pressure of toluene is given by the relation: ln Psat = 13.9987 - 3096.52/(219.48 + t), where t is in oC and Psat in kPa. What is the latent heat of vaporization at 107.2oC?
  11. Two components A and B form a maximum boiling azeotrope at 90oC and 760 mm Hg. The composition of azeotrope is 60 mole % A. The vapor pressure of A and B at 90oC are 600 and 300 mm Hg respectively. Calculate the Margules constants and plot ln g A Vs. xA.
  12. An experimental determination of a VLE state for ethanol - toluene system gave the following results. Vapor pressure at 45oC: Ethanol = 173 mm Hg, Toluene = 75.4 mm Hg, x1 = 0.3 y1 = 0.634, PT = 183 mm Hg. Calculate (i) the liquid phase activity coefficient (ii) does the liquid phase exhibit positive or negative deviation from ideal solution behavior?

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M.Subramanian, Lecturer, Chemical Engg, SVCE, Sriperumbudur - 602105, Tamil Nadu, INDIA