Asgn #48: Intermolecular Forces Name Dec. 13, 2016 1. 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 2. Which of the following substances will have the highest boiling point (all are nonpolar)? a) methane (MW=16) b) pentane (MW=70) c) ethane (MW=30) d) butane (MW=58) 3. Which of the following substances will have the lowest boiling point? a) neon (Ne) b) water c) ammonia (NH3 this is a polar molecule) d) helium (He) 4. 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. 5. Rank the following liquids in order of increasing boiling points, from lowest to highest: He / NH3 / Ar / N2 (NH3 is a polar molecule) a) He < N2 < Ar < NH3 b) He < Ar < N2 < NH3 c) NH3 < Ar < N2 < He d) NH3 < N2 < Ar < He 6. 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 7. The smallest repeat unit of a crystalline solid is called: a) a point group b) a lattice point c) a unit cell d) a crystalline element 1
8. 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. 9. The type of solid which is characterized as positive ions embedded in a sea of delocalized electrons is called: a) a metallic solid b) a ionic solid c) a molecular solid d) a covalent (network) solid 10. Diamond (pure carbon) would be classified as which type of solid: a) a metallic solid b) a ionic solid c) a molecular solid d) a covalent (network) solid 11. 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 little with pressure. 12. Chlorine has a critical temperature of 144 C and a critical pressure of 77 atm. Under which of the following conditions would Cl2 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 13. 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. 2
14. The term used to describe resistance to flow of a liquid is: a) surface tension b) capillary action c) viscosity d) vapor pressure 15. Which response lists intermolecular forces (between molecules of comparable size) in order of increasing strength? a) London < dipole < H-bond < ionic b) dipole < London < H-bond < ionic c) H-bond < ionic < dipole < London d) ionic < H-bond < London < dipole 16. 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. 17. Arrange these substances in order of INCREASING boiling point: Xe, H2, H2O, LiCl, H2S. (Water is polar, LiCl is ionic, the remaining substances are non-polar.) a) Xe < H2 < H2O < LiCl < H2S b) Xe < H2 < H2S < H2O < LiCl c) H2 < Xe < H2S < H2O < LiCl d) H2 < Xe < H2O < H2S < LiCl 18. Which is the weakest intermolecular force among a group of molecules of comparable molecular weight (molar mass)? a) dipole-dipole b) London c) ionic bonding d) hydrogen bonding 19. Which of the following pure substances exhibits hydrogen bonding? a) NH3 b) H2S c) HCl d) CH4 3
20. Base your answer to the following question on the graph below, which shows the vapor pressure curves for liquids A and B. Which liquid will evaporate more rapidly? Explain your answer in terms of intermolecular forces. 21. Using the information below state evidence that indicates that NH3 has strong IMFs than CF4. 4
24. Carbon forms molecular compounds with some elements from Group 16. Two of these compounds are carbon dioxide, CO2, and carbon disulfide, CS2.Carbon dioxide is a colorless, odorless gas at room temperature. At standard temperature and pressure, CO2(s) changes directly to CO2(g). Carbon disulfide is formed by a direct reaction of carbon and sulfur. At room temperature, CS2 is a colorless liquid with an offensive odor. Compare the intermolecular forces in CO2 and CS2 at room temperature. 25. At room temperature, F2 and Cl2 are gases, Br2 is a liquid, and I2 is a solid. This is because: a) dipole-dipole interactions increase with molecular size. b) dipole-induced dipole interactions increase with molecular size. c) dispersion interactions increase with molecular size. d) dispersion interactions increase with molecular size and polarity increases with molecular size. 26. 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) The H-O covalent bond is much stronger than the H-S and H-Se bonds. b) The intermolecular attractive forces are much greater in water than in hydrogen sulfide and hydrogen selenide. c) The water molecule is lighter than the other two molecules. d) Water has the lowest molecular weight. 5