ch11_11ed_exercises - Visualizing Concepts 471 Know the...

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Unformatted text preview: Visualizing Concepts 471 , Know the difference between crystalline and amorphous solids, and be able to explain the differences between primitive cubic, body—centered cubic, and face-centered cubic unit cells. . Classify solids based on their bonding / intermolecular forces and understand how difference in bonding relates to physical properties. VISUALIZING CONCEPTS 11.] Does the following diagram best describe a crystalline 800 cq solid, liquid, or gas? Explain. [Section 11.1] U‘IO\\1 GOO GOO Vapor pressure (mm Hg) ,4; O O ‘1 300 " 200 hf 100 e 11.2 (a) What kind of intermolecular attractive force is " CQ shown in each of the following cases? (b) Predict which 930 _10 10 30 50 5't two interactions are stronger than the other two. 0 1* [Section 11.2] Temperature ( C) 11.5 The following molecules have the same molecular for- .- CQ mula (C3H80), yet they have different normal boiling to a . J J J j J (c) J ,1 a J oints, as shown. Rationalize the difference in boilin < t .H. t. .a p g 1Y “t ' “‘3 points. [Sections 11.2 and 11.5] :h h (b) w,gjlum (d) 9JJIJJ“ J. g . _ e I J )e- or 3ft _ 11.3 The molecular models of glycerol and 1-propanol are (a) Propoanol (b) Ethy} methyl ether List CQ given here. 97'2 C 10'8 C nd . _ 11.6 The phase diagram of a hypothetical substance is shown niC CQ below. ltS. . .th‘ 1.0 les. E (a) Glycerol (b) 1-propanol E s 0.5 -' / Do you expect the viscosity of glycerol to be larger or g ion smaller than that of 1-propanol? Explain. [Section 11.3] E 5315 11 . ~ . . ' -4 Usmg the followmg graph of C82 data, determine (a) the CQ approximate vapor pressure of C82 at 30 °C, (b) the tem— 0 perature at which the vapor pressure equals 300 torr, 0 100 200 300 400 (C) the normal boiling point of C82. [Section 11.5] Temperature (K) (a) Estimate the normal boiling point and freezing 5. point of the substance. Se (b) What is the physical state of the substance under the tiCal following conditions? (i) T = 150 K, P = 0.2 atm ub’ (ii) T = 100 K, P = 0.8 atm 5 (iii) T = 300 K, P = 1.0 atm (c) What is the triple point of the substance? [Section 11.6] '1... 472 CHAPTER 11 Intermolecular Forces, Liquids, and Solids 11.7 Niobium(li) oxide crystallizes in the following cubic 11.8 13} What kindclf packing arrangement is seen in the a CQ unit cell. CQ companying. photo? {'b') What is the coordinattun “uric. ber of each orange-in the interior of'the-Stack? (I:} ”Eat ' orangempresefits'an argon atom; what category uf Solih is represented? [Sections 11.7 and 11.3] d l"'-\ 1“: (*- 4—... a" .,_ ‘ .Y “ - ‘63. 1‘ (a) How many niobium atoms and how many oxygen atoms are within the unit cell? (b) What is the empirical formula of niobium oxide? (c) Is this a molecular, covalent-network, or ionic solid? [Sections 11.7 and 11.8] EXERCISES Molecular Comparisons of Gases, Liquids, and Solids 11.9 List the three states of matter in order of (a) increasing room temperature. (a) Is the density of olive oil more or molecular disorder and (b) increasing intermolecular less than 1.00 g/cm3? (b) The density of olive oil in its attractions. (c) Which state of matter is most easily liquid phase does vary with temperature. Do you think compressed? olive oil would be more dense or less dense at higher 11.10 (a) How does the average kinetic energy of molecules temperatures? Explain. CQ compare with the average energy of attraction between 11.12 Benzoic acid, C6H5COOH, melts at 122 °C. The density molecules in solids, liquids, and gases? (b) Why does (Q in the liquid state at 130 °C is 1.08 g/cm3. The density of increasing the temperature cause a solid substance solid benzoic acid at 15 °C is 1.266 g/cma. (a) In which of to change in succession from a solid to a liquid to a gas? these two states is the average distance between mole- (C) What happens to a gas if you put it under extremely cules greater? (b) Explain the difference in densities at high pressure? the two temperatures in terms of the relative kinetic efl' . . . . . . . ergies of the molecules. 11.11 If you mix olive 011 With water, the ohve 011 Will float on CQ top of the water. The density of water is 1.00 g/cm3 at Intermolecular Forces N 11.13 Which type of intermolecular attractive! force operates atomic weight 84, boils at 120.9 K, whereas C12, molecu-t between (a) all molecules, (b) polar molecules, (c) the lar weight about 71, boils at 238 K. (d) Acetone 130115 a hydrogen atom of a polar bond and a nearby small elec- 56 °C, whereas 2-methylpropane boils at —12 °C. tronegative atom? 11.14 Based on what you have learned about intermolecular fi C|H3 CQ forces, would you say that matter is fundamentally at— CH3— C—CH3 CH3— CH—CHs tracted or repulsed by other matter? Acetone Z-Methylproparle 11.15 Describe the intermolecular forces that must be over- . f CQ come to convert each of the following from a liquid or 11.17. (a) Wlmt is meant by the term petarizabflity? (b)'w1fifiho solid to a gas: (a) 12, (b) CH3CH20H. (c) ste. the following atoms Would you expect to be m05tp011: 11.16 What type of intermolecular force accounts for the fol- izable:'N, R As,- Sb? Explain. 1c) Put the following "3“, H CQ lowing differences in each case? (a) CH3OH boils at cules in orderof increasing pdlafizabflity: GECLIF _.ilil-.Ig 65 °C, CHgSH boils at 6 °C. (b) Xe is liquid at atmos- sicfi4,_-SiHi,_-aind Cream. (a) Predict the order of 190‘ - pheric pressure and 120 K, whereas Ar is a gas. (c) Kr, points of the substances in part (c). e or 1 its 1ink rher tSity y of h of ole— es at . en- 1115 True or false: (a) The more polarizable the molecules, the stronger the dispersion forces between them. (b) The boiling points of the noble gases decrease as you go down the column in the periodic table. (c) In general, the smaller the molecule, the stronger the dispersion forces. (d) All other factors being the same, dispersion forces between molecules increase with the number of electrons in the molecules. ’ii-fiII-Which member of the following pairs has the larger London dispersion forces: (a) H20 or H25, (b) C02 or CO, (C) SiH4 or GeHi? 1120 Which member of the following pairs has the stronger intermolecular dispersion forces: (a) Brz or 02, (b) CH3CH2CH2CH25H OI' CH3CH2CH2CH2CH28H, (c) CHgCHzCHZCl or (CH3)2CHCl? F1111 Butane and 2-methylpropane, whose space-filling mod- cQ els are shown, are both nonpolar and have the same molecular formula, yet butane has the higher boiling point (—0.5 °C compared to *11.7 °C). Explain. (a) Butane (b) 2—Methylpropane 11.22 Propyl alcohol (CH3CH2CH20H) and isopropyl alcohol CQ [(CH3)2CHOH], whose space-filling models are shown, have boiling points of 97.2 °C and 82.5 °C, respectively. Explain why the boiling point of propyl alcohol is higher, even though both have the molecular formula of C3H80. (a) Propyl alcohol (b) Isopropyl alcohol 5 Ylsimsity and Surface Tension Exercises 473 “9-3 (a) What atoms must a molecule contain to participate in hydrogen bonding with other molecules of the same kind? (b) Which of the following molecules can form hydrogen bonds with other molecules of the same kind: CHst CHBNHz, CHgOH, CHgBr? 11.24 Rationalize the difference in boiling points between the CQ members of the following pairs of substances: (a) HF (20 °C) and HCl (~85 °C), (b) CHc13 (61 °C) and CHBr3 (150 0C), (C) sz (59 OC) and ICl (97 °C). 11.25 Ethylene glycol (H.C)C:H2CI'IZOHL the major substance in antifreeze, has a normal boiling point of 198 0C. By comparison, ethyl alcohol (CH3CHZOH) boils at 78 0C at atmospheric pressure. Ethylene glycol dimethyl ether (CI-130CH2CH20C313) has a normal boiling point of 83 0C, and ethyl methyl ether (CHgCHZOCH3) has a normal bOiling point of 11 °C. (a) Explain why replace- ment of a hydrogen on the oxygen by CH3 generally re— sults in a lower boiling point. (b) What are the major factors responsible for the difference in boilir g points of the two ethers? 11.26 Identify the types of intermolecular forces present in each of the following substances, and select the sub- stance in each pair that has the higher boiling point: (a) C6H14 0r C8H18, (b) C3Hg or CH3OCH3, (c) HOOH or HSSH, (d) NHzNHz or CH3CH3. 11.27 Look up and compare the normal boiling points and CQ normal melting points of H30 and H28. (a) Based on these physical properties, which substance has stronger intermolecular forces? What kind of intermolecular forces exist for each molecule? (b) Predict whether solid H28 is more or less dense than liquid HES. How does this compare to H20? Explain. (c) Water has an unusual- ly high specific heat. Is this related to its intermolecular forces? Explain. 11.28 The following quote about ammonia (NH3) is from a CQ textbook of inorganic chemistry: “It is estimated that 26% of the hydrogen bonding in NH3 breaks down on melting, 7% on warming from the melting to the boiling point, and the final 67% on transfer to the gas phase at the boiling point.” From the standpoint of the kinetic energy of the molecules, explain (a) why there is a decrease of hydrogen—bonding energy on melting and (b) why most of the loss in hydrogen bonding occurs in the transition from the liquid to the vapor state. 11.21?) (a) Explain why surface tension and viscosity decrease CQ with increasing temperature. (b) Why do substances with high surface tensions also tend to have high viscosities? “-30 (a) Distinguish between adhesive forces and cohesive CQ forces. (b) What adhesive and cohesive forces are in- volved when a paper towel absorbs water? (c) Explain the cause for the U-shaped meniscus formed when a _ water is in a glass tube. “3'“ Explain the following observations: (a) The surface ten- CQ sion of CHBr3 is greater than that of CHCl3. (b) As tem- perature increases, oil flows faster through a narrow tube. (c) Raindrops that collect on a waxed automobile hood take on a nearly spherical shape. ((1) Oil droplets that collect on a waxed automobile hood take on a flat shape. 11.32 Hydrazine (HZNNHZ), hydrogen peroxide (HOOH), CO and water (H20) all have exceptionally high surface ten— sions compared with other substances of comparable molecular weights. (a) Draw the Lewis structures for these three compounds. (b) What structural property do these substances have in common, and how might that account for the high surface tensions? 474 Ph_ase Changes 11.33 11.34 CHAPTER 11 Name the phase transition in each of the following situ- ations, and indicate whether it is exothermic or en- dothermic: (a) When ice is heated, it turns to water. (b) Wet clothes dry on a warm summer day. (c) Frost appears on a window on a cold winter day. (d) Droplets Of water appear on a cold glass of beer. Name the phase transitiOn in each of the following situ- ations, and indicate whether it is exothermic or en- dothermic: (a) Bromine vapor turns to bromine liquid as it is cooled. (b) Crystals of iodine disappear from an evaporating dish as they stand in a fume hood. (c) Rub- bing alcohol in an open container slowly disappears. (d) Molten lava from a volcano turns into solid rock. I 11.35 Explain why the heat of fusion of any substance is gen- CD 11.36 CQ 11.37 11.38 erally lower than its heat of vaporization. Ethyl chloride (C2H5Cl) boils at 12 °C. When liquid C2H5Cl under pressure is sprayed on a room-temperature (25 °C) surface in air, the surface is cooled considerably. (a) What does this observation tell us about the specific heat of C2H5Cl(g) as compared with C2H5Cl(l)? (b) As- sume that the heat lost by the surface is gained by ethyl chloride. What enthalpies must you consider if you were to calculate the final temperature of the surface? For many years drinking water has 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 35 °C to 20 0C by the evaporation of 60 g of water? (The heat of vaporization of water in this tem- perature range is 2.4 k]/ g. The specific heat of water is 4.18 I/g-K.) Compounds like CC12F2 are known as chlorofluorocar- bons, or"CFCs. These compounds were once widely used as refrigerants but are now being replaced by com- pounds that are believed to be less harmful to the envi- ronment. The heat of vaporization of CC12F2 is 289 I/ g. What mass of this substance must evaporate to freeze 200 g of water initially at 15 °C? (The heat of fusion of water is 334 I/ g; the specific heat of water is 4.18 I/g-K.) YapoLPressure and Boiling Point 11.43 CQ 11.44 CQ Intermolecular Forces, Liquids, and Solids ' 11.39 Ethanol (C2H5OH) melts at —114 "C and boils at 73 a 11.40 Its density is 0.789 g/mi.. The enthalpy of fusion ‘ ethanol is 5.02 kJ/mol, and its enthalpy of vapoflZafit-Tf is 38.56 kJ/mol. The specific heats of solid and “Gilli: ethanol are 0.97 I/g-K and ZBI/g-K, respectiWl (a) How much heat is required to convert 25.0 9, if ethanol at 25 °C to the vapor phase at '78 °C? (b) How much heat is required to convert 5.00 1.. of ethane} at ~140 °C to the vapor phase at '78 °C? The fluorocarbon compound C2C13F3 has a normal boil- ing point of 47.6 °C. The specific heats of C2C13F3(l) and C2Cl3F3(g) are 0.91 J/g-K and 0.67 I/g-K, respectively The heat of vaporization for the compound is 27.49 kl/mol. Calculate the heat required to convert 50.0 g of C2C13F3 from a liquid at 10.00 °C to a gas at 85.00 °C. 11.41 (a) What is the significance of the critical pressure of a CQ 11.42 CQ substance? (b) What happens to the critical temperature of a series of compounds as the force of attraction be- tween molecules increases? (c) Which of the substances listed in Table 11.5 can be liquefied at the temperature of liquid nitrogen (—196 °C)? The critical temperatures (K) and pressures (atm) of a series of halogenated methanes are as follows: .—_———————I- Compound CC13F CClez CC1F3 CF4 Critical Temperature 471 385 302 227 Critical Pressure 43.5 40.6 38.2 37.0 (a) List the intermolecular forces that occur for each compound. (b) Predict the order of increasing intermol- ecular attraction, from least to most, for this series of compounds. (c) Predict the critical temperature and pressure for CCL; based on the trends in this table. Look up the experimentally determined critical temp‘eratums and pressures for C04, using a source such as the .CRC Handhpok of Chemistry and Physics, and suggest a tease“ for any discrepancies. 0 Explain how each of the following affects the vapor pressure of a liquid: (a) volume of the liquid, (b) surface area, (c) intermolecular attractive forces, (d) tempera- ture, (e) density of the liquid. A liquid that has an equilibrium vapor pressure of 130 torr at 25 °C is placed into a 1-L vessel like that shown in Figure 11.22. What is the pressure difference shown on the manometer, and what is the composition of the gas in the vessel, under each of the following conditions: (a) Two hundred mL of the liquid is introduced into the vessel and frozen at the bottom. The vessel is evacuated and sealed, and the liquid is allowed to warm to 25 °C. (b) Two hundred milliliters of the liquid is added to the vessel at 25 °C under atmospheric pressure, and after a few minutes the vessel is closed off. (c) A few mL Of the liquid is introduced into the vessel at 25 °C while it has a pressure of 1 atm of air in it, without allowing any of the air to escape. After a few minutes a few drOPS 0f liquid remain in the vessel. 11.45 11.46 (a) Place the following substances in order- of increasmg volatility: CH4,CBr4,CH2C12, CH3C1,'CHBr3-, and cHzBr? Explain. (b) How 'do the boiling points vary through thls series? True or false: (a) CBr4 is more volatile than CCl4. (b) CBr4 has a higher boiling point than CCl4. (c) CBr4 has weaker intermolecular forces than CC14' ’ (d) CBr4 has a higher vapor pressure at the same tem perature than CCl4. 1i 11 “:1 4‘7 (a) Two pans of water are on different burners of a stove. I ‘03 One pan of water is boiling vigorously, while the other is boiling gently. What can be said about the tempera- ture of the water in the two pans? (b) A large container of water and a small one are at the same temperature. What can be said about the relative vapor pressures of the water in the two containers? 1,48 Explain the following observations: (a) Water evapo— CE] rates more quickly on a hot, dry day than on a hot, humid day. (b) It takes longer to boil water for tea at high altitudes than at lower altitudes. 1 ll J11; USing the vapor-pressure curves in Figure 11.24, (a) esti- mate the boiling point of ethanol at an external pressure of 200 torr; (b) estimate the external pressure at which ethanol will boil at 60 °C; (c) estimate the boiling point of diethyl ether at 400 torr; (d) estimate the external pressure at which diethyl ether will boil at 40 °C. Phase Diagrams Exercises 475 11.50 Appendix B lists the vapor pressure of water at various external pressures. (a) Plot the data in Appendix B, vapor pressure (torr) vs. temperature (C). From your plot, estimate the vapor pressure of water at body temperature, 37 °C. (b) Explain the significance of the data point at 760.0 torr, 100 0C. (C) A city at an altitude of 5000 ft above sea level has a barometric pressure of 633 torr. To what temper— ature would you have to heat water to boil it in this city? ((1) A city at an altitude of 500 ft below sea level would have a barometric pressure of 774 torr. To what temperature would you have to heat water to boil it in this city? (e) For the two cities in‘ parts (c) and (cl), compare the aver-age kinetic energies of the water molecules at their boiling points. Are the kinetic energies the same or different? Explain. 11.51 (a) What is the significance of the critical point in a CQ phase diagram? (b) Why does the line that separates the gas and liquid phases end at the critical point? 11.52 (a) What is the significance of the triple point in a phase diagram? (b) Could you measure the triple point of water by measuring the temperature in a vessel in which water vapor, liquid water, and ice are in equilibri— um under one atmosphere of air? Explain. 11.51"- Refer to Figure 11.27(a), and describe all the phase changes that would occur in each of the following cases: (a) Water vapor originally at 0.005 atm and —0.5 °C is slowly compressed at constant temperature until the final pressure is 20 atm. (b) Water originally at 100.0 °C and 0.50 atm is cooled at constant pressure until the temperature is ~10 °C. §tr_ut:tures of Solids 11.54 Refer to Figure 11.27(b), and describe the phase changes (and the temperatures at which they occur) when C02 is heated from —80 °C to —20 °C at (a) a constant pressure of 3 atm, (b) a constant pressure of 6 atm. 11.55 Sketch a generic phase diagram for a substance that has a more dense solid phase than a liquid phase. Label all regions, lines, and points. 11.56 The normal melting and boiling points of 02 are —218 OC and ~183 °C respectively. Its triple point is at —219 °C and 1.14 torr, and its critical point is at —119 °C and 49.8 atm. (a) Sketch the phase diagram for 02, showing the four points given and indicating the area in which each phase is stable. (b) Will 02(5) float on 02(l)? Explain. (c) As it is heated, will solid 02 sublime or melt under a pressure of 1 atm? ..I_ i . . . ”47/ (a) Draw a picture that represents a crystalline solid at C0. the atomic level. (b) Now draw a picture that represents an amorphous solid at the atomic level. “-58 Amorphous silica has a density of about 2.2 g/cm3, CQ Whereas the density of crystalline quartz is 2.65 g/cm3. -_ Account for this difference in densities. {Ll}? ——_. ‘1 Tausonite, a mineral composed of Sr, 0, and Ti, has the cubic unit cell shown in the drawing. (a) What is the chemical formula of this mineral? (b) It is easy to see that Ti is coordinated by six oxygen atoms, because the Ti atom is located at the center of the unit cell. To see the full coordination environment of the other ions, We have to consider neighboring unit cells. How many oxygens are coordinated to strontium? o Strohtium 6 Oxygen 9 Titan...
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