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Chem 2 Chpt 11Intermolecular forces Problems


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11.9 List the three states of matter in order of (a) increasing molecular disorder and (b) increasing intermolecular attractions.
(a) solid<liquid<gas (b) gas<liquid<solid
11.13Which type of intermolecular attractive force operates between (a) all molecules, (b) polar molecules (c)the hydrogen atom of a polar bond and a nearby small electronegative atom?
(a)London disperson forces (b) dipole-dipole and London dispersion forces (c) dipole-dipole forces and in some cases hydrogen bonding
11.15 Describe the intermolecular forces that must be overcome to convert each of the following from a liquid to a gas: (a) Br2 (b)C.H3..0.H (c) H2.S
(a)nonpolar covalent molecule; London dispersion forces only (b) polar covalent molecule with O-H bonds; hydrogen bonding, dipole-dipole forces and London dispersion forces (but not hydrogen bonding)
11.17 (a)What is meant by the term polarizability? (b) Which of the following atoms would you expect to be most polarizable: O, S, Se or Te ? Explain. (c) Pu the following molecules in order of increasing polarizability: Ge.Cl4 , C.H4, Si.Cl4, Si.H4, and
(a) polarizability is the ease with which the charge distribution in a molecules can be distorted to produce a transient dipole (b) Te is most polarizable because its valence electrons are farthest from the nucleus and least tightly (c) in order of increasing polarizability : C.H4< Si.H4< Si.Cl4< Ge.Cl4< Ge.Br4 (d) THe magnitudes of London dispersion forces and thus the boiling points of molecules increase as polarizability increases, the order of increasing boiling points is the order of increasing polariazability given in (c)
11.19 Which member of the following pairs has the larger London dispersion forces: (a) H2.O or H2.S, (b)C.O2 or CO, (c) C.H4 or Si.H4 ?
(a)H2.S (b)C.02 (c)Si.H4
11.23 (a) What molecular features must a molecule have to participate in hydrogen bonding with other molecules of the same kind? (b) Which of the following molecules can form hydrogen bonds with other molecuels of the same kind: C.H3.F, C.H3.N.H2, C.H3.O
(a)molecules with N-H, O-H, and F-H bonds form hydrogen bonds with like molecules (b)C.H3.N.H2 and C.H3.O.H
11.25 Rationalize the difference in boiling points between the members of the following pairs of substances: (a) H.F (20 C) and H.Cl (-85 C), (b) C.H.Cl3 (61 C) and C.H.Br3 (150 C), (c) Br.2 (59 C) and I.Cl (97 C)
(a) H.F has the higher boiling point because hydrogen bonding is stronger than dipole-dipole forces. (b) C.H.Br3 has the higher boiling point because it has the higher molar mass, indicating greater polarizability and stronger dispersion forces. (c) I.Cl is polar, givening it dipole-dipole forces that are absent for the nonpolar Br2
11.27 How are the following observatins related to the ability of water to form hydrogen bonds? (a) Ice is less dense than liquid water. (b) Water has a high specefic heat, meaning it requires a large amount of heat to produce a temperature increase of 1
(a)Hydrogen bonding occurs in both water and ice. In water, molecules are close together and moving. Hydrogen bonds are constantly broken and new ones formed. In ice, molecules adopt an ordered structure with four hydrogen bonds per molecule. These interactions produce a network structure with more open space between molecules than in the liquid state and corresponding lower density for the solid than the liquid. (b) raising the temperature of a substance means increasing the average kinetic energy of its molecules. A large amount of heat must be added to water to break its strong hydrogen bonds and increase its average kinetic energy and temperature.
11.29 (a) Why do surface tension and viscosity decrease with increasing temperature? (b) Why do substances with high surface tensions also tend to have high viscosities?
(a) as temperature increases, the number of molecules with sufficent kinetic energy to overcome intermolecular attractive forces increases, and viscosity and surface tension decrease (b)the same attractive forces that cause surface molecules to be difficult to separate(high surface tension) cause molecules elsewhere in the sample to resist movement relative to eacher other (high viscosity)
11.31 Explain the following observations: (a) The surface tension of C.H.Br3 is greater than that of C.H.Cl3. (b) As temperature increases , oil flows through a narrow tube. (c) Raindrops that collect on a waxed automobile hood take on a nearly spherical
(a) C.H.Br3 has a higher molar mass, is more polarizable, and has stronger dispersion forces, so the surface tension is greater. (b) as temperature increases, the viscosity of the oil decreases because the aaverage kinetic energy of the molecules increase. (c)adhesive forces between polar water and nonpolar car wax are weak, so the large surface tnesion of water draws the liquid into the shape of the smallest surface area, or sphere
11.33 Name the phase transition in each of the following situations, and indicate whether it is exothermic or endothermic: (a) When water is colled, it turns to ice. (b) Wet clothes dry on a warm summer day. (c) Frost appears on a window on a cold winter
(a) freezing, exothermic (b) evaporation, endothermic (c) desposition, exothermic
11.35 Explain why the heat of fusion of any substance is generally lower than its heat of vaporization.
melting does not require separation of molecules, so the energy requirement is smaller than for vaporization, where molecules must be separated.
11.37 For many years drinking water hasa been cooled in hot climates by evaporating it from the surfaces of canvas bags or porous clay pots. How many grams of water can be cooled from 35C to 22C by the evaporation of 50g of water?(heat of vaporization =
2.2x10^3 g H2.O
11.39 Ethanol ( C2.H5.O.H) melts at -114C and boils at 78C. The enthalphy of fusion of ethanol is 5.02 kJ/mol, and its enthaly of vaporization is 38.56 kJ/mol. The specific heats of solid and liquid ethanol are .97 J/g-K and 2.3 J/g-K, respectively. How
105 kJ
11.41 (a)What is the significance of the critical pressure of a substance? (b) What happens to the critical temperature of a series of compounds as the force of attraction between molecules increase?
(a) the critical pressure is the pressure required to cause liquefaction at the critical temperature (b)as the force of attraction between molecules increases, the critical temperature of the compound increases

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