Unit Five: Intermolecular Forces Name MC Question Practice April 14, 2017 1. Which of the following should have the highest surface tension at a given temperature? 2. The triple point of compound X occurs at a temperature of a. 50 C b. -10 C c. 80 C d. 29 C e. 23 C 3. The normal boiling point of X is most likely a. 80 C b. 90 C c. 50 C d. 28 C e. 22 C 4. Which of the following hydrocarbons has the highest boiling point? a) These are all gases and do not boil b) C 3H 8 c) CH 4 d) C 4H 10 e) C 2H 6 5. The correct order for increasing boiling point among the noble gases is: 1. He 2. Ne 3. Ar 4. Kr 5. Xe This phenomenon is best explained in terms of. a. Hund s rule b. London dispersion forces c. hydrogen bonding d. dipole-dipole interaction 1
6. As the pressure increases, the melting point of compound X will a. decrease and then increase b. stay the same c. decrease d. increase 7. Place the following in order of increasing strength 1. hydrogen bonding 2. covalent bonding 3. London Dispersion forces a. 3, 2, 1 b. 1, 3, 2 c. 3, 1, 2 d. 2, 1, 3 8. When the adhesive forces between a liquid and the walls of a capillary tube are greater than the cohesive forces within the liquid A. the liquid level in a capillary tube will rise above the surrounding liquid and the surface in the capillary tube will have a convex meniscus. B. the liquid level in a capillary tube will rise above the surrounding liquid and the surface in the capillary tube will have a concave meniscus. C. the liquid level in a capillary tube will drop below the surrounding liquid and the surface in the capillary tube will have a convex meniscus. D. the liquid level in a capillary tube will drop below the surrounding liquid and the surface in the capillary tube will have a concave meniscus. 9. At room temperature, F 2 and Cl 2 are gases, Br 2 is a liquid, and I 2 is a solid. This is because: a. polarity increases with molecular size. b. dipole-induced dipole interactions increase with molecular size. c. dipole-dipole interactions increase with molecular size. d. dispersion interactions increase with molecular size and polarity increases with molecular size. e. dispersion interactions increase with molecular size. 10. The boiling point of CH 4 is much lower than that of HF. This is because: a) of ion-dipole interactions in CH 4. b) HF is more polarizable. c) of hydrogen bonding in HF. C) CH 4 is polar. e) of dipole-dipole interactions in CH 4. 11. The boiling point of water is about 200 C higher than one would predict from the boiling points of hydrogen sulfide and hydrogen selenide. One may explain this apparent anomaly by which of the following? a. Water is less polar than hydrogen sulfide and hydrogen selenide. b. Water has the lowest molecular weight. c. The H-O covalent bond is much stronger than the H-S and H-Se bonds. d. The intermolecular attractive forces are much greater in water than in hydrogen sulfide and hydrogen selenide. e. The water molecule is lighter than the other two molecules. 2
12. The vapor pressure of a liquid increases exponentially with increasing temperature chiefly because a. the strength of the intermolecular forces increases. b. the fraction of high energy molecules increases much faster than the average energy. c. the average molecular mass increases. d. atmospheric pressure increases. 13. State why the normal melting point of ICl(27.2 C) is so much higher than that of Br 2 (-7.2 C). The molecules of both substances have the same number of electrons. a. the ICl molecules have a lower molecular weight b. ICl molecules are polar c. the ICl molecules undergo hydrogen bonding d. iodine in ICl is more electronegative than bromine in Br 2 e. the Cl atom in the ICl molecule is more polarizable than the Br atom in the Br 2 molecule. 14. Based on the following information: CF 4, Molecular Weight 87.99, Normal Boiling Point = -127.8 C CCl 4, Molecular Weight 153.8, Normal Boiling Point = 76.72 C Which IMFs explain this trend? a) dipole-dipole forces (permanent dipoles) b) dispersion (or London) forces c) repulsive forces d) ion-dipole forces 15. Why is the normal boiling point of hydrogen fluoride so much higher than that of hydrogen chloride, the hydride of the next element in group VIIA? a. the HF molecules have a lower dipole moment. b. HCl molecules are non-polar. c. chlorine in HCl is more electronegative than fluorine in HF. d. the HF molecules undergoes a higher degree of hydrogen bonding than HCl 16. Based on the following information: CF 4, Molecular Weight 87.99, Normal Boiling Point = -127.8 C CCl 4, Molecular Weight 153.8, Normal Boiling Point = 76.72 C Which of the above substances would have the higher equilibrium vapor pressure assuming that both substances are in the liquid state at the same temperature? a) CCl 4 b) CF 4 and CCl 4 would have the same vapor pressure b) CF 4 d) impossible to determine from the information given 17. Based on intermolecular interactions, which of the following should have the highest boiling point? a. CH 4 b. CHCl 3 c. H 2S d. CH 3OH 18. Hydrogen bonding is unimportant in a) ice formation b) the liquid properties of water c) DNA structure d) liquid CH 4 e) liquid HF 19. Which one of the following statements is incorrect? a. Dispersion (London) forces are the weakest type of intermolecular interactions. b. The strong intermolecular attractions in H 2O result from hydrogen bonding. c. The boiling point of H 2S is lower than H 2O. d. The boiling point of non-polar substances tends to decrease with increasing molecular weight. 3
20. Which of the following phase diagrams is consistent with the sublimation of a solid at room temperature (22 o C) and atmospheric pressure? 21. Methanol, CH 3OH (bp: 65 o C), boils nearly 230 o higher than methane, CH 4 (bp: -164 o C). What intermolecular forces are responsible for the higher boiling point of methanol? a. dispersion forces b. hydrogen bonds c. induced dipole-induced dipole d. ion-dipole e. dipole-induced dipole The next two questions refer to 4 liquids, all of which have the molecular formula C 4H 10O and which have the following boiling points: A (117.5 o C); B (82.9 o C); C (34.6 o C); D (99.5 o C). 22. The liquid likely to have the highest vapor pressure at 25 o C is: a) A b) B c) C d) D e) All four substances would have the same vapor pressure since they have the same molecular weight. 23. The intermolecular attractive forces of these are likely to be ordered: a) A > D > B > C b) B > D > A > C c) C > B > D > A d) D > C > B > A e) none of the above 24. Which of the following compounds feature intermolecular attractions in the liquid or solid state? a. argon b. diamond c. water d. sodium chloride e. none of these 25. Which of the following has the lowest boiling point? a. F 2 b. Cl 2 c. Br 2 d. I 2 26. The intermolecular forces that are most significant in accounting for the high boiling point of liquid water relative to other substances of similar molecular weight are the: a) ion-ion attractions b) London dispersion forces c) hydrogen bonding forces d) dipole-dipole attractions 4
27. Drops of water and ethanol are placed on a warm stove, and the ethanol drop is seen to evaporate more rapidly. The graph below includes the vapor pressures of ethanol and water. Which curve corresponds to ethanol? a. A b. B c. C d. D e. none of the above 28. Decreasing the external pressure will: a. increase the vapor pressure of a liquid. b. markedly decrease the freezing point of a liquid. c. increase the boiling point of a liquid. d. decrease the boiling point of a liquid. e. weaken the intermolecular forces in a liquid. 29. Which of the following substances will have the highest boiling point? a) methane (MW=16) b) butane (MW=58) c) ethyl alcohol (MW=46) d) methyl alcohol (MW=32) 30. Which of the following substances will have the lowest boiling point? a) neon b) water c) ammonia d) helium 31. Identify the INCORRECT statement below: a) When the vapor pressure of a liquid equals the surrounding pressure, the liquid boils. b) The boiling point is the temperature at which the vapor pressure of the liquid equals the surrounding pressure. c) The normal boiling point is the temperature at which the vapor pressure of the liquid equals 1 atm. d) The vapor pressure of a liquid increases as the temperature of the liquid increases. e) Easily vaporized liquids are called volatile liquids, having low vapor pressures. 32. Based on interaction strength between ions, which of the following compounds has the highest melting point? a) CaCl 2 b) NaCl c) NaF d) MgO 33. Rank the following liquids in order of increasing boiling points, from lowest to highest: He / NH3 / Ar / N2 a) He < N 2 < Ar < NH 3 b) He < Ar < N 2 < NH 3 c) NH 3 < Ar < N 2 < He d) NH 3 < N 2 < Ar < He 5
34. The interaction responsible for the cohesive intermolecular forces of liquid nitrogen is: a) hydrogen bonding b) the London dispersion force c) dipole-dipole interaction d) covalent bonding 35. Identify the INCORRECT statement below: a) The vapor pressure of liquid water at 100 C is 760 Torr (1 atm). b) The normal boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals 1 atm. c) The boiling point of a liquid increases as the surrounding pressure decreases. d) Vapor pressure of a liquid increases as the temperature increases. e) A liquid boils when its vapor pressure equals the surrounding pressure. 36. Which of the following intermolecular forces is INCORRECTLY assigned as the principal force in the compound given? a) CCl 4, London b) NH 3, London c) HF, H-bonding d) CH 3OH, H-bonding e) H-Br, dipole 37. According to the following phase diagram for a substance X, which of the following statements is FALSE? a) The normal boiling point of X is 184 C. b) At 25 C, X will boil if the pressure is lowered enough. c) X is liquid at 120 C and 1 atm. d) The melting point of X varies with change in pressure. 38. Which of the following is NOT true of covalent (network) solids? a) The units which occupy the lattice points are atoms. b) The inter-unit forces are covalent bonds. c) They typically exhibit low melting points. d) They are usually very hard. e) They are usually poor electrical conductors. 39. Chlorine has a critical temperature of 144 C and a critical pressure of 77 atm. Under which of the following conditions would Cl 2 most likely be a liquid? a) 125 C, 70 atm b) 125 C, 30 atm c) 150 C, 70 atm d) 150 C, 30 atm 40. How much energy would it take to boil 36.0 g of water at 100 o C? a. 81.4 KJ b. 1470 KJ c. 1.13 KJ d. 0.0123 KJ 6
41. The normal boiling point of ether is 35 C. Comparing ether and water, at the same temperature, which statement below is TRUE? a) The vapor pressure of both liquids are the same. b) The vapor pressure of ether is greater than that of water. c) The vapor pressure of water is greater than that of ether. d) The vapor pressure of both liquids are equal to the temperature. 42. The term used to describe resistance to flow of a liquid is: a) surface tension b) capillary action c) viscosity d) vapor pressure e) vaporization 43. Which response lists interparticle forces (between molecules of comparable size) in order of increasing strength? a) London < ionic < H-bonds < dipole b) dipole < London < H-bond < ionic c) H-bond < ionic < dipole < London d) ionic < H-bond < London < dipole e) London < dipole < H-bond < ionic 44. On the following typical phase diagram, which statement is INCORRECT? a) Point A corresponds to sublimation/deposition. b) Point B corresponds to the critical point, where all three phases coexist. c) Point C corresponds to the liquid phase of the substance. d) At a higher temperature and pressure than point D, the substance exists as a supercritical fluid. e) Raising the pressure from point E to point C causes the substance to condense. 45. Arrange these substances in order of INCREASING boiling point: Xe, H 2, H 2O, LiCl, H 2S. a) Xe < H 2 < H 2O < LiCl < H 2S b) Xe < H 2 < H 2S < H 2O < LiCl c) H 2 < Xe < H 2S < H 2O < LiCl d) H 2 < Xe < H 2O < H 2S < LiCl 46. When water is measured in a plastic graduated cylinder, a reverse meniscus is observed because a. the hydrogen bonds between water molecules are greater than the attractions between the water molecules and the walls of the container. b. the viscosity of the water is greater than the viscosity of the plastic. c. surface tension of the water prevents it from "beading up" inside the container. d. the molecules of water are forced closer together because of London forces. e. the attractive forces between the water molecules and the walls of the container are greater than the attractive forces between the water molecules. 7
47. Refer to Figure 11-1. The temperature at point b is the a. critical point. b. triple point. c. absolute freezing point. d. normal freezing point. e. normal boiling point. 48. Refer to Figure 11-1. The transition from Phase I to Phase III is called a. melting. b. freezing. c. sublimation. d. evaporation. e. condensation. 49. The Hvap is related to the strength of intermolecular forces. Which of the following has the lowest Hvap? a. C 3H 8 b. C 6H 12 c. C 3H 7OH d. C 3H 7NH 2 e. C 8H 18 50. Given the following information for C 6H 6, calculate its molar heat of vaporization. At 300 K, the vapor pressure is 92.47 mmhg, and at 320 K, the vapor pressure is 225.1 mmhg. a) 208 kj/mol b) 16.4 kj/mol c) 10.3 kj/mol d) 35.5 kj/mol 51. The heat of vaporization of benzene, C 6H 6, is 30.8kJ/mol at it boiling pint of 80.1ºC. How much energy is required to vaporize 102g of benzene at it boiling point? a. 0.302kJ b. 23.6kJ c. 24.2kJ d. 40.2kJ e. 31400kJ 52. The standard enthalpy of vaporization of water, H 2O, ΔH vap = 40.7 kj mol -1 at 373 K. Assuming this value to remain constant at temperatures close to 373 K, use the Clausius-Clapeyron equation to estimate the vapor pressure of liquid water at 80 C. a) 95.8 kpa b) 48.2 kpa c) 97.9 kpa d) 101 kpa 53. The vapour pressure of liquid carbon disulfide, CS 2, is 23.5 kpa at 280 K and 51.3 kpa at 300 K. Calculate the enthalpy of vaporization of carbon disulfide at 290 K. a) 17.9 kj mol -1 b) 27.3 kj mol -1 c) 97.2 kj mol -1 d) 94.1 kj mol -1 54. A coffee pot contains 300.0 grams of water at 100 o C. How many kilojoules of heat are required to evaporate completely all the water??h vap of water is 40.7 kj/mole. a) 0.133kJ b) 12200kJ c) 133kJ d) 678kJ 8
55. HCl and NaCl have about the same molecular mass, but have vastly different boiling points. Which will have the higher boiling point and why? a) NaCl will have the higher boiling point because it has ionic intermolecular forces. b) HCl will have the higher boiling point because it has hydrogen bonding forces. c) NaCl will have the higher boiling point because it has dipole-dipole intermolecular forces. d) HCl will have the higher boiling point because it has dipole-dipole intermolecular forces. 56. The experimentally measured vapor pressure of SO 2 at -25 o C is 49.5 kpa and at 0 o C is 155 kpa. Use the Clausius- Clapeyron equation to determine the enthalpy of vaporization, ΔH vap. a) 3.55 kj/mol b) 25.6 kj/mol c) 67.8 kj/mol d) 130. kj/mol 57. Arrange these compounds in order of increasing boiling points. NH3, LiF, CO2, CH3Cl a) CH 3Cl < LiF < CO 2 < NH 3 b) NH 3< CO 2< CH 3Cl < CH 3F c) CO 2 < CH 3Cl < NH 3< LiF d) LiF < NH 3< CH 3Cl < CO 2 58. Which of the following would you expect to be lower for octane, C 8H 18, than for hexane, C 6H 14? (A) the critical temperature (B) the normal boiling point (C) the heat of vaporization at the normal boiling point (D) the vapor pressure of the liquid at 25 o C (E) none of the above would be expected to be higher for hexane than for octane. 59. At room temperature and pressure, substance A is a solid, substance B is a liquid, and substance C is a gas. According to the ideas of the kinetic theory, at room temperature and pressure, intermolecular forces in: (A) C are much stronger than those in B. (B) A are somewhat weaker than those in B. (C) C are somewhat stronger than those in A. (D) B are very strong compared to the average kinetic energy of its molecules. (E) C are very weak compared to the average kinetic energy of its molecules. 60. A positive slope for a region of a heating curve indicates that in that region. a. no energy is being absorbed by the system b. energy is being given off by the system, but it cannot be measured c. energy is being absorbed by the system and is being used for a phase change d. additional data is needed to explain this observation e. energy is being absorbed by the system and is being used to increase the temperature Questions 61-63 are based on the information given below. In an experiment, a solid 1 molar sample of Substance A was gradually heated by a source of constant energy for several hours and the temperature was measured periodically. At the end of the heating period, Substance A had been converted to the gas phase. The heating curve produced by this experiment is shown below. 9
61. During the course of the experiment, there was a period of time when the solid phase of Substance A was in equilibrium with the liquid phase. At what temperature did this occur? a) Between 100K and 150K b) At 150K c) Between 150K and 250K d) At 250K e) Between 250K and 350K 62. Based on the data given in the heating curve, which of the following statements is NOT true regarding Substance A? a) The boiling point of Substance A is 250K. b) The freezing point of Substance A is 150K. c) The heat of vaporization of Substance A is greater than the heat of fusion. d) Substance A is a liquid at room temperature. e) The intermolecular forces exhibited by Substance A are weaker than those of water. 63. During the course of the experiment, Substance A was gradually heated from 100K to 350K. When the temperature reached 250K, the energy absorbed by Substance A a) was used to change from liquid to gas phase. b) was used to change from gas to liquid phase. c) was used to change from solid to liquid phase. d) was used to change from liquid to solid phase. e) was reduced to zero. 64. When the following compounds are kept at the same temperature, the compound expected to evaporate most quickly is a) C 8H 18 b) C 8H 17OH c) C 8H 17NH 2 d) C 6H 14 e) C 7H 15COOH 65. Which of the following will have the greatest change in its boiling point if the pressure at which it is boiled is changed from 1.00 atm to 0.900 atm? (The numbers in parentheses are the heats of vaporization in kilojoules per mole.) a) Water (43.9) b) Ammonia (21.7) c) Methane (8.2) d) Bromine (15.0) e) Fluorine (5.9) 66. C 30H 62 is a nonpolar compound that is a solid at room temperature and water is highly hydrogen bonded but is a liquid because a) water molecules are very light. b) water molecules ionize easily. c) the 62 hydrogen atoms in C 30H 62 allow for many instantaneous dipoles that exceed the attractive force of a hydrogen bond. d) C 30H 62 is so large that it cannot melt. e) C 30H 62 has a lower melting point if dissolved in nonpolar hexane. 10
67. On the basis of this heating curve, which of the following statements is true? a) The heat of fusion and heat of vaporization are about equal. b) The heat capacities of the solid, liquid, and gas are approximately equal. c) The heat capacity of the gas is greater than that of the liquid. d) The heat capacity of the gas is greater than the heat of fusion. e) The heat of vaporization is less than the heat of fusion. Use the phase diagram below for questions 68-71. 68. Determine, from the phase diagram, the maximum temperature at which this compound will sublime. a) 100 C b) 230 C c) 115 C d) 95 C e) It cannot sublime 69. What is the normal boiling point of this compound? a) 95 C b) 100 C c) 50 C d) 180 C e) 150 C 70. At 125 C and 1.50 atm of pressure this substance will be a) a liquid b) a solid c) a gas d) a solid and liquid in equilibrium e) a gas and liquid in equilibrium 71. Which pair of temperatures and pressures will produce a supercritical fluid? a) 150 C and 2.00 atm b) 95 C and 1.00 atm c)145 C and 2.30 atm d) 10 C and 0.15 atm e) 250 C and 2.00 atm 11
72. A student observed that a small amount of acetone sprayed on the back of the hand felt very cool compared to a similar amount of water. You explanation of this phenomena should be that a) acetone has a lower viscosity and transfers heat quanta better b) water has a higher heat capacity than acetone, therefore, retaining more heat c) the higher vapor pressure of acetone results in more rapid evaporation and heat loss d) The observed effect is not real and is only imagined For questions 73 and 74 consider the following heating curve of a hypothetical substance: 73. What is the boiling point of the substance? (a) 0 C (c) 12 C (b) 50 C (d) 75 C 74. What state of matter is the substance at 50 C? (a) gas (c) solid (b) liquid (d) not enough information 75. The phase changes are not associated with temperature increases (as shown on the heating curve above) because the heat energy is used up to. A) increase the velocity of molecules B) break forces between molecules C) rearrange atoms within molecules D) increase the density of the sample E) break intramolecular bonds 76. The enthalpy change when 1.00 mol of water at 25.0 C is converted to steam at 115.0 C is kj. The specific heats of ice, water, and steam are 2.09 J/g-K, 4.18 J/g-K, and 2.08 J/g-K, respectively. For H 2O, Hfus = 6.01 kj/mol, and Hvap = 40.67 kj/mol A) 432.0 B) 7.08 x 10 3 C) 47.36 D) 46.9 E) 41.06 77. How much energy (kj) is required to convert a 15.5 g ice cube at -5.0 C to water vapor at 180 C? A) 56 B) 9.0 x 103 C) 11 D) 49 E) 27 78. If 10.0 kj of heat are added to a 15.5 g ice cube at -5.00 C, what will be the resulting state and temperature of the water? A) vapor, 134 C B) liquid, 13.9 C C) solid, -4.85 C D) liquid, 72.0 C E) vapor, 103 C 12