课程名称︰普通化学乙 课程性质︰必修 课程教师︰李弘文 开课学院：理学院 开课系所︰心理系 考试日期（年月日）︰2008/12/17 考试时限（分钟）：100 是否需发放奖励金：yes （如未明确表示，则不予发放） 试题 : - 1 - General Chemistry Midterm Exam (II)A 2008.12.17 系别：________ 姓名：________________ 年级：________ 学号：________________ Read these instructions carefully before you start!! Total Time: 100 mins (10:30 AM – 12:10 PM) (1). There are 3 sections (True/False, Multiple Choice and Integrated Questions), with total 120 points. This exam has total 8 pages. (2). Only the answers shown in the assigned boxes will be graded. (3). Correct answers must be accompanied with the correct sign and unit. (4). Formula/constant sheet is given at the end of the exam. (5). You are not allowed to use any other notes/sheets in this exam. (6). You are not allowed to use cell phone during the exam, even just for the calculator function. (7). You can only use your own calculator. (8). If you write this exam with pencil, you are not eligible for any re-grade. (9). Show all the intermediate steps in how you work out the answers to the integrated questions (10). You are obligated to follow the rules of NTU’s Academic Integrity. Spend a minute to look over the whole exam before you start, so you can plan your time well. Good Luck ! - 2 - I. True/False Section: (20%, 2 pts each) 1.T The average kinetic energy of the N2 and CO2 gases is the same under the same temperature. 2.T If the compression factor, Z, is less than one for a given gas, the van der Waals coefficient "a" is dominant for real gases. 3.F HI has a lower boiling point than HBr. 4.F CHF3 has a lower boiling point than CF4. 5.F Viscosity usually increases with increasing temperature. 6.T The ability of water to "wet" paper is due to hydrogen bonding between water molecules and surface molecules in the paper. 7.T Molecular solids are held together by weak intermolecular forces. 8.F A semiconductor is a substance with a resistance that increases with increasing temperature. 9.T In the rock-salt structure (NaCl), the cations (Na+) occupy all the octahedral holes. 10.T Isotropic liquids have viscosities that are the same in every direction. I. II. III. total II. Multiple Choice Section: Pick one best answer. (60 %, 2 pts each) - 3 - 1.B The hybrid orbitals used by the underlined atoms in , from left to right, respectively, are A) sp3 and sp2. B) sp2 and sp2. C) sp2 and sp. D) sp and sp. 2.A Which of the following molecules is (are) polar? (a) I3+ (b) I3- (c) N3- (d) S32- A) (a) and (d) B) (a) and (b) C) (b) and (d) D) (c) and (d) 3.C In NO, the unpaired electron occupies what type of molecular orbital? A) 3σ B) 4σ* C) 2π* D) 1π 4.C Order the following molecules according to increasing C-F bond length: A) CF+ B) CF C) CF- 5.C Which of the bond angle at the central atom of the following molecules and ions is the largest? A) NO2- B) O3 C) N3- D) BrO3- 6.B Predict whether each of the following molecules is polar. A) BF3 B) PCl3 C) CS2 D) CCl4 7.C What is the shape of the ClO3- ion? A) linear B) bent C) trigonal pyramidal D) square pyramidal 8.A If the collisions between the molecules and the walls of the container are not elastic, how would the pressure of the gas be affected? A) would decrease the pressure B) would increase the pressure C) would not affect the pressure 9.A A MO orbital for a heteronuclear diatomic is given by Ψ MObonding = CAΦA + CBΦB If A is more electronegative than B then you would predict that A) CA > CB B) CA = CB C) CA < CB D) CA = -CB 10. B How many σ- and π-bonds, respectively, are there in peroxyacetylnitrate, ? A) 9 and 2 B) 10 and 2 C) 10 and 1 D) 8 and 4 11.D A sample of a gas weighing 15.1 g occupies 2.25 L at 1.75 atm and 20.0℃. If the empirical formula of the gas is NO2, what is the molecular formula? A) N5O10 B) N3O6 C) NO2 D) N2O4 12.D Ammonium nitrate can decompose according to the following equation: NH4NO3(s) N2O(g) + 2H2O(g) How many liters of gas are produced by decomposition of 160 g of ammonium nitrate at -25°C and 86.0 kPa? A) 48.0 B) 14.5 C) 57.6 D) 144 13.A A plot of the Maxwell distribution for the same gas against temperature shows that A) at low temperatures, most molecules have speeds close to their average speed. B) as the temperature increases, a high proportion of molecules have very slow speeds. C) as the temperature decreases, the spread of speeds widens. D) as the temperature decreases, a high proportion of molecules have very high speeds. 14.B Consider the following van der Waals coefficients: - 4 - Which of the following gases has the smallest attractive forces? A) ammonia B) helium C) neon D) hydrogen Gas a, L2·atm·mol-2 b. L·mol-1 ammonia 4.17 0.0371 helium 0.034 0.0237 neon 0.211 0.0171 hydrogen 0.244 0.0266 15. 送分 Which molecules of the following gases will have the greatest average kinetic energy? A) CO2 at 1 atm and 298 K B) N2 at 1 atm and 298 K C) He at 0.1 atm and 298 K 16.C Which molecules of the following gases will have the greatest root-mean-square speed? A) N2 at 1 atm and 273 K B) He at 0.1 atm and 273 K C) H2 at 0.5 atm and 273 K D) All the molecules have the same root mean square speed 17.C Consider the following statements: 1. Real gases act more like ideal gases as the temperature increases. 2. When n and T are constant, a decrease in P results in a decrease in V. 3. At 1 atm and 273 K, every molecule in a sample of a gas has the same speed. 4. At constant T, CO2 molecules at 1 atm and H2 molecules at 5 atm have the same average kinetic energy. Which of these statements is true? A) 2 and 3 B) 1 and 2 C) 1 and 4 D) 3 and 4 18.C Under what conditions do real gases act least like ideal gases? A) high temperatures and low pressures. B) high pressures and low molar masses. C) low temperatures and high pressures. D) high temperatures and high pressures. 19.D Which of the following can form intermolecular hydrogen bonds? A) B) C) D) 20.B Which of the following is the strongest intermolecular force between molecules? A) dipole-dipole (stationary) C) dipole-dipole (rotating) B) hydrogen bonding D) London 21.C What are all the intermolecular forces that are responsible for the existence of ice? A) dipole-dipole and London forces B) London forces C) dipole-dipole, London forces, and hydrogen bonding D) dipole-dipole and ion-ion 22.B How many calcium and fluorine ions are there in the fluorite unit cell shown below? A) 4 Ca2+ and 2 F- B) 4 Ca2+ and 8 F- C) 2 Ca2+ and 4 F- D) 2 Ca2+ and 8 F- 23.C As shown in 22, what are the coordination numbers of Ca2+ and F- ions, respectively, in fluorite? A) 6 and 8 B) 4 and 8 C) 8 and 4 D) 6 and 4 24.B The solid ZnS has a radius ratio of 0.45 and adopts the zinc-blende structure. What is the coordination number of Zn in ZnS? A) 12 B) 4 C) 8 D) 2 25.D Which of the following compounds is likely to adopt the cesium chloride (CsCl) structure? A) AgCl, ρ = 0.62 B) MgO, ρ= 0.51 C) CaO, ρ= 0.71 D) TlCl, ρ= 0.90 26.B If a cubic unit cell of an ionic compound has A cations at the corners and the face centers and X anions in the centers of the edges, what is the empirical formula of the compound? A) AX B) A4X3 C) AX2 D) A2X3 27.C Which has the strongest intermolecular forces? A) N2 B) H2S C) H2O D) CH4 28.B Order the following gases according to increasing mass density: N2; NH3; NO2. The temperature and pressure are the same for all three samples. A) N2< NH3< NO2 B) NH3< N2< NO2 C) NO2< N2< NH3 D) N2< NO2< NH3 29.C What hybrid orbitals are used by the nitrogen (N) atoms in urea,? A) sp B) sp2 C) sp3 D) dsp3 30.D Which of the following molecules might form the conductivity polymer? A) B) C) D) - 5 - III. Integrated Questions (40%) 1. (a). What are the major assumptions we made in deriving gas kinetic theory? (4pts) - 6 - 1. An ideal gas consists of discrete particles (could be molecules or atoms). 2. The particles are far apart and occupy zero volume. 3. The particles are in constant motion (Newtonian type physics describes those motions) 4. The particles couldn’t care less about each other or the container that holds them (no attractive forces). 5. The particles do collide with one another and the sides of the container. 6. Energy is conserved. (A particle may gain energy if another loses an equal amount.) (b). What is the root-mean-square speed of ethane (C2H6) molecules at -20°C? (4pts) (c). Plot the three-dimensional Maxwell speed distribution of CH4( ), O2(---) gas at 300K. (4pts) 2. (a) In the table below, fill in the blanks about (1). the number of atoms per unit cell, and (2) the fraction of occupied volume in the following three types of metal crystal packing. (3). Which of the following packing is the closet pack structure? (4pts) 2a(3) face‐centered cubic(fcc) (b) Silver metal crystallizes in a cubic closest packed structure. The face centered cubic unit cell edge is 409 pm. Calculate the density of the silver metal (atomic weight of sliver is 107.87 g/mol). (2pts) 3. (a) Why thermotropic liquid crystals can only exist in certain temperature range? (2pts) What happens when the temperature is higher and lower than this liquid crystal range? (2pts) 2b length of unit cell edge = 409 pm = 4.09 x 10-8 cm Density = ()235-8107.8746104.0910×××=10.5 g/cm3 (b) The liquid crystals of p-azoxyanisole (117℃ to 137℃), and (E)-4-tert-butyl-N -(4-methoxy- benzylidene)aniline (21℃ to 47℃) have different liquid crystal temperatures. Their chemical structures are shown below. Propose possible reasons for the different liquid crystal temperatures. (2pts) (3a) The ordering in a liquid crystal might extend along only one dimension, with the material being essentially disordered in the other two directions. Thermotropic phases are those that occur in a certain temperature range. If the temperature is raised too high, thermal motion will destroy the delicate cooperative ordering of the LC phase, pushing the material into a conventional isotropic liquid phase. At too low a temperature, most LC materials will form a conventional (though anisotropic) crystal. Many thermotropic LCs exhibit a variety of phases as temperature is changed. (3b) The multiple bond structure of p-azoxyanisole gives rise to the rigid rod-like nature of the molecule. The alternating double bonds that allow electrons to be delocalized extend from one ring across the bridging N atoms to the other ring. To maintain the delocalization, the phenyl rings do not rotate about the Q-N axis. Thus, the entire molecule is like a stiff, flat rod. Only the CH3 groups rotate. Another feature that enhances the tendency to form liquid crystalline materials is the inclusion of the aromatic rings. The π-bonds in aromatic rings show a strong tendency to stack one upon another; this helps orient the molecules in the liquid crystalline array. Disrupting some of the London interactions that the molecule will have with its neighbors, thus allowing the molecules more freedom to move with respect to each other. It would be expected that the bulky t-butyl group (-C(CH)3) of (E)-4-tert-butyl-N-(4-methoxybenzylidene)aniline would help to disrupt the orderly packing of the molecule. 4.(a) In the homonuclear O2 molecules, the Eπ2p is higher than Eσ2p. Experiments have shown that O2 is paramagnetic (i.e. have un-paired electrons). Draw the energy diagram of molecular orbitals in O2 with the electrons filled, and use them to explain why O2 is paramagnetic. (4pts) (b) Fill the blanks in the table. (2pts) Paramagnetic/diamagnetic bond order O2 Paramagnetic 2 O2- Paramagnetic 1.5 (c) Arrange these three molecules in the order of increasing bond length (from small to large). (2pts) O22- diamagnetic 1 - 8 - 5. The atomic orbitals of two 2pz are shown below. (a). Why the linear combination of these two orbital forms the sigma molecular orbitals (MOs), while the combination of 2py (and 2px) orbitals form pi MOs? (3pts) (b). Plot the bonding MO σ2p, and anti-bonding MO σ2p* (4pts) O2 <O2- <O22- σ orbitals: the sign doesn’t change as you rotate the orbitals about the internuclear axis.(head-to- head) π orbitals: the sign changes as you rotate the orbitals around the internuclear axis.(i.e.they are not symmetrical about the z-axis) (side-to-side) —End of Exam— -- 让记忆抛在背後你听我说： 神色是熟悉可不承认是寂寞 偶尔有点黯然可并不是不是 悲哀。其实我仍然是乐观的 不知道你到底在忧虑些甚麽 --

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