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Phase Equilibrium: Two Components

Phase Equilibrium: Two Components. Contributions by: John L. Falconer & Will Medlin Department of Chemical and Biological Engineering University of Colorado Boulder, CO 80309-0424 Supported by the National Science Foundation. 1.0. 1.0. 1.0. 1.0. 1.0. y A. x A. 0.5. 0.5. 0.5. 0.5.

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Phase Equilibrium: Two Components

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  1. Phase Equilibrium:Two Components Contributions by: John L. Falconer & Will MedlinDepartment of Chemical and Biological EngineeringUniversity of ColoradoBoulder, CO 80309-0424 Supported by the National Science Foundation

  2. 1.0 1.0 1.0 1.0 1.0 yA xA 0.5 0.5 0.5 0.5 0.5 xA 0 0 0 0 0 P P P P P yA yA xA xA yA xA yA The pressure increases for a 50/50 vapor mixture of A and B that is initially at a low pressure. The liquid is ideal. Which plot corresponds to how xA and yA change with pressure at constant temperature if PAsat > PBsat? C A B D E

  3. 1.0 1.0 1.0 1.0 1.0 yB xB 0.5 0.5 0.5 0.5 0.5 xB 0 0 0 0 0 P P P P P yB yB xB yB xB xB yB The pressure increases for a 50/50 vapor mixture of A and B that is initially at a low pressure. The liquid is ideal. Which plot corresponds to how xB and yB change with pressure if PAsat > PBsat? A B C D E

  4. Which is the VLE line that most likely connects liquid and vapor phases in equilibrium for a benzene-hexane mixture? A B C None of these x x Isotherm for 60-40 benzene/hexane mixture x x x x A P B C V

  5. Which is the VLE line that most likely connects liquid and vapor phases in equilibrium for a pentene-octene mixture? A B C None of these Isotherm for 70-30 pentene/octene mixture x A P x x x B x x C x x D Isotherm for 40-60 pentene/octene mixture V

  6. P-x P-x P-y P-x P-x P-x P P P P P P P-x P-y P-y P-y P-y P-y xA, yA xA, yA xA, yA xA, yA xA, yA xA, yA 2 & 6 1, 4, & 6 2 & 5 2, 3, & 5 3 & 5 Which of these diagrams are not possible? 2 1 3 4 5 6

  7. Mg and Si form the compound Mg2Si. At constant pressure, what is the composition of the system when xSi= 0.4 and T = 1000 K? One solid phase Pure Si and Mg Si and Mg2Si 1600 liquid T (K) 1200 Mg2Si 800 0.5 1.0 0 mole fraction of Si Mg Si

  8. Mg and Si form the compound Mg2Si. At constant pressure, what is the composition of the system when xSi= 0.6 and T = 1000 K? One solid phase containing Mg and Si Two solid phases: 40% Si, 60% Mg2Si Two solid phases:60% Si, 40% Mg2Si Two solid phases:each contain Si & Mg 1600 liquid 1200 T (K) Mg2Si 800 0.5 1.0 0 mole fraction of Si Mg Si

  9. This figure shows saturated liquid and saturated vapor lines for a 2-component system. Which of these are equilibrium compositions and temperature? x1= 0.6, y1=0.9, 245°C x1= 0.6, y1=0.3, 210°C x1= 0.9, y1=0.6, 200°C x1= 0.6, y1=0.3, 250°C

  10. A tank contains a 50/50 mixture of A and B (yA = 0.6). As the vapor is removed and the liquid boils away, the mole fraction of A in the liquid phase __________. increases decreases remains the same

  11. A liquid mixture (x1 = 0.4) evaporates at constant pressure by increasing the temperature. The first bubble has a composition of y1 = 0.7 because component 1 is more volatile and preferentially evaporates. As the last drop of liquid is evaporating, which is correct about the mole fraction of component 1 in the vapor phase? y1 = 0.7 y1 = 0.4 y1 > 0.7 0.4 < y1 < 0.7

  12. A liquid mixture (x1 = 0.4) evaporates at constant pressure by increasing the temperature. The first bubble has a composition of y1 = 0.7 because component 1 is more volatile and preferentially evaporates. As the last drop of liquid is evaporating, which is correct about the mole fraction of component 1 in the liquid phase? x1= 0.4 x1 > 0.4 x1 <0.7 x1 <<< 0.4

  13. A closed system has methanol and ethanol in vapor-liquid equilibrium at 1 bar and 65°C. The temperature of the system is raised to 70°C at 1 bar. If two phases are still present, how do the methanol mole fractions change for each phase? (Note: Tsat(methanol) = 65°C, Tsat(ethanol) = 78°C) xm increases, ym decreases xm increases, ym increases xm and ym do not change xm decreases, ym decreases xm decreases, ym increases

  14. We want to separate 50/50 mixtures of C6 isomers in the gas phase. As the temperature was lowered, your technician observed that n-hexane (n-C6) condensed before 2,2, dimethylbutane (DMB). Can this happen? Yes, if n-C6 has a lower vapor pressure than DMB Yes, if n-C6 has a higher vapor pressure than DMB No, because both species have to condense It depends on the system pressure as to whether one or two species condense.

  15. A mixture of n-hexane and acetone were in the liquid phase in a piston-cylinder at 1 bar pressure. As the temperature increased, your technician observed that acetone evaporated first. Can this happen? Yes, if acetone has the higher Psat Yes, if n-hexane has the higher Psat No, both species evaporate It depends on the system pressure as to whether one or two species evaporate

  16. A mixture of n-hexane and acetone were in the liquid phase in a piston-cylinder at 1 bar pressure. As the pressure decreased, your technician observed that acetone evaporated first. Can this happen? Yes, if acetone has the higher Psat Yes, if n-hexane has the higher Psat No, both species evaporate It depends on the system pressure as to whether one or two species evaporate

  17. A mixture of water and acetone was placed in an open beaker in a room. The next morning, 90% of the acetone had evaporated, but none of the water had evaporated. Can this happen? Yes, if acetone has the higher Psat Yes, if n-hexane has the higher Psat No, both species evaporate It depends on the system pressure as to whether one or two species evaporate

  18. At 100°C, PAsat = PBsat. Will this system exhibit an azeotrope at 100°C? Yes No Maybe…need more information.

  19. Which statement is not correct? A binary mixture that has a minimum boiling point azeotrope ____________. has a maximum pressure azeotrope has one composition where the boiling point does not change as liquid evaporates cannot be modeled by a modified Raoult’s Law allows for either component 1 or 2 to be enriched in the vapor phase, depending on the liquid composition has activity coefficients greater than one

  20. A liquid mixture of 50 mol% n-pentane (Psat= 5 bar) and 50 mol% n-heptane (Psat = 1 bar) is at high pressure. The mixture is partially vaporized by isothermally lowering the pressure to just below 3 bar. Which statement is correct? n-heptane is enriched in the gas phase n-pentane is enriched in the gas phase The gas phase has a 50/50 composition No vapor forms

  21. Often, wine or beer is added to soup that is then simmered. When the soup is ready to be served, what has happened to the alcohol? It all evaporates It all remains in the soup Some of it evaporates

  22. ________ is the driving force for component A to move from liquid to vapor in order to reach equilibrium. Pressure Entropy Enthalpy Concentration Gibbs free energy

  23. 1.0 mol of CH4 at 1 bar and 50°C is mixed with 1.0 mol of O2 at 1 bar and 50°C. The final mixture is at 2.0 bar and 50°C. Assume ideal gases. The Gibbs free energy change is _______. positive negative zero

  24. An n-butane/n-heptane mixture is in vapor-liquid equilibrium. The liquid composition is 30% n-butane. Which of these vapor compositions (% n-butane) are not possible? 20% 40% 60% 80% All of these compositions are possible

  25. Consider a system at equilibrium that contains n-hexane and water, which are immiscible in the liquid phase. Which set of phases could not exist? Two Liquids (hexane + H2O) Hexane liquid and two vapors (hexane + H2O) Two Liquids (hexane + H2O) and hexane vapor H2O liquid and two vapors (hexane + H2O) None of the above

  26. Consider a 1 L constant-volume container with n-hexane in VLE. If half the volume is liquid and 0.1 L of liquid H2O is added to the container, what happens? Assume constant temperature and that water is immiscible with n-hexane. Some hexane evaporates Some hexane condenses All the H2O evaporates Some water evaporates and some hexane condenses All the hexane evaporates

  27. An ideal liquid solution that is 30% A, 30% B, and 40% C is heated at a constant temperature until 80% of the original liquid has evaporated. Which component would you expect to have completely evaporated at that point? Component A Component B Component C None of them PAsat > PBsat> PCsat

  28. Assume ideal gas and ideal solution behavior for the A-B system: PAsat= 1.5; PBsat= 1.0 bar ; T = 70°C What is the total pressure at equilibrium above a liquid that is 60% A and 40% B? 2.5 bar 1.5 bar 1.2 bar 1.0 bar None of the above

  29. Which of the following statements is NOT true at an azeotrope? xA = yA xA = xB None of the above

  30. Which of the following statements is NOT true at an azeotrope? xA = yA None of the above

  31. At VLE, Which is the correct equation to use when solving for the liquid phase fugacity of component 2 using an equation of state? x2*g2*P x2*f2L*P x2*f2L*Psat x2*g2*Psat None of the above

  32. One mole of component A is in VLE at 1 bar and 75°C. One mole of B is added to form a mixture, and the pressure is isothermally increased to 2 bar. What is the state of the system? The vapor pressure of B at 75°C is 2 bar. Assume A and B form an ideal solution. VLE All liquid All vapor

  33. Which of the following is true for a binary azeotrope at low pressure? The activity coefficients of the two components are the same The vapor pressures of the two components are the same The value of the vapor pressures multiplied by the activity coefficients are the same None of these

  34. Are there conditions in which liquid water (or solid ice) at barospheric pressure will not have a vapor phase partial pressure when in contact with nitrogen? (Assume the system is below the normal boiling point of nitrogen). No. Yes, if the temperature is low enough Yes, if the temperature is high enough

  35. You want to completely condense a vapor containing 50% methanol(1) and 50% ethanol(2). What is the minimum pressure at which the condenser mustoperate at 105°C?  At 105°C: P1sat = 1.8 bar, P2sat = 1.2 bar 3.0 bar 1.8 bar 1.5 bar 1.2 bar

  36. At what temperature is 59 mol% ethane liquid not in equilibrium with a vapor? 335 °F 275 °F 315 °F 400 °F M 89 mol% C2 77 mol% C2 59 mol% C2 CC2H6 P 27 mol% C2 CC7H16 100 500 0 300 700 T (°F)

  37. 59 mol% ethane liquid is in equilibrium with what ethane mol% vapor composition? 77 89 27 All of those shown A & B M 89 mol% C2 77 mol% C2 59 mol% C2 CC2H6 P 27 mol% C2 CC7H16 100 500 0 300 700 T (°F)

  38. A vapor with 59% ethane is in equilibrium with which phase? 89% 77% 59% 27% None of the above M 89 mol% C2 77 mol% C2 59 mol% C2 CC2H6 P 27 mol% C2 CC7H16 100 500 0 300 700 T (°F)

  39. When the interaction parameter, kij,increases, for a fixed liquid phase, fixed temperature system, the equilibrium pressure ________. increases decreases remains the same

  40. A liquid mixture containing species A & B is boiled by increasing the temperature at constant pressure. The saturation pressure is greater for A than for B.What happens? xA increases and yA increases xA increases and yAdecreases xAdecreases and yAdecreases xAdecreases and yA increases

  41. 140 130 T-y 1 120 110 T-x Temperature 1 100 90 80 70 0 0.2 0.4 0.6 0.8 1 X , Y 1 1 ¼ 1/3 2/3 ¾ What is the fraction of this mixture that is liquid?

  42. In a bubble pressure calculation using a EOS, the mole fractions of liquid are known, and the mole fractions of vapor must be calculated by iteration by guessing the pressure. After the first iteration, Syi > 1. For the next iteration, _______________. raise the pressure lower the pressure keep the pressure the same but change the composition

  43. A EOS spreadsheet is used to calculate VLE for a binary mixture (x1= 0.9) with a non-ideal liquid phase and a non-ideal gas. Which statement about the fugacity coefficients is most likely to be correct? = = < >

  44. 6 mol A and 4 mol B are in equilibrium at 100°C and3.0 bar. A and B are completely immiscible in theliquid phase. Their vapor pressure at 100°C are: Which phases are present? Liquid B and vapor of A + B Two liquids Two liquids in equilibrium with vapor All vapor Liquid A and vapor of A + B

  45. 6 mol A and 4 mol B are in equilibrium at 100°C and2.0 bar. A and B are completely immiscible in theliquid phase. Their vapor pressure at 100°C are: Which phases are present? Liquid B and vapor of A + B Two liquids Two liquids in equilibrium with vapor All vapor Liquid A and vapor of A + B

  46. A gas phase mixture at 100°C is 75 % A and 25 % B. As pressure increases isothermally, liquid A starts to condense at 1.6 bar. At 2.4 bar liquid B starts to condense. What are the vapor pressures of A and B? PAsat= 1.6 bar, PBsat= 2.4 bar PAsat= 1.2 bar, PBsat= 1.6 bar PAsat= 1.6 bar, PBsat= 1.2 bar PAsat= 1.8 bar, PBsat= 0.6 bar PAsat= 1.2 bar, PBsat= 1.2 bar

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