课程名称︰普通化学丙 课程性质︰必修 课程教师︰郑淑芬 开课学院：工 开课系所︰机械系 考试日期（年月日）︰99/05/06 考试时限（分钟）：2hr 是否需发放奖励金：是 谢谢 （如未明确表示，则不予发放） 试题： General Chemistry, 2nd Mid-term Exam Single Choice Questions (16%; 2 points per question, -0.5 points per mistake) 1. If the orbitals of two atoms overlap and interact with constructive interference, the resulting increase in wave density results in a: (a) bonding molecular orbital (b) antibonding molecular orbital (c) valence band (d) conduction band 2. "Doping" pure silicon with gallium results in a _____ material. (a) ionic conductor (b) n-type semiconductor (c) p-type semiconductor (d) semimetal 3. Which of the following substances has the highest boiling point? (a) C3H6 (b) Ar (c) CH2Cl2 (d) HF 4. Which substance has the lowest vapor pressure: (a) CH3OCH3 (b) C3H8 (c) CH3CH2OH (d) C3H6 5. Under constant volume conditions, the change in internal energy equals the: (a) entropy (b) insulation capacity (c) enthalpy (d) heat flow 6. Calculate ΔS for the reaction: 2N2O(g) → 2N2(g) + O2(g) S in J/mol K for: N2O(g)=240.0, N2(g)=191.5, O2(g)=205.0 (a) +157 J/K (b) -157 J/K (c) +108 J/K (d) -480 J/K 7. Which of the following compounds having the same structure as diamond has the largest band gap? (a) Ge (b) GaAs (c) ZnSe (d) CuBr 8. Consider the combustion of glucose (C6H12O6). This reaction is: (a) spontaneous at all temperatures (b) non-spontaneous at all temperatures (c) spontaneous towards higher temperatures (d) non-spontaneous towards lower temperatures Multiple Choice Questions (21%, 3 points per question, -0.5 points per mistake) 9. Which of the following diatomic molecules is paramagnetic? (a) B2 (b) C2 (c) N2 (d) O2 10. Which one of the following molecules has a planar geometry? (a) PCl3 (b) BF3 (c) XeF4 (d) SF4 11. A new alloy is designed for use in a car radiator. If the 17.6kg radiator required 8.69 x 10^5 J of heat to warm from 22.1℃ to 155.8℃, what is the specific heat of the new alloy? (a) 0.365 J/g℃ (b) 8.27 J/g℃ (c) 0.00491 J/g℃ (d) 1.70 J/g℃ 12. What is the oxidation state of the metal ion which forms a metal oxide compound that crystallized with metal ions occupying half of the octahedral holes in a cubic close-packed array of oxide ions? (a) 1 (b) 2 (c) 3 (d) 4 13. Freonc12 is used as refrigerant. Its heat of vaporization is 289 J/g. What mass of Freon 12 must evaporate in order to freeze 100 g of water initially at 18℃? (The heat of fusion of water is 334 J/g; the geat capacity of water per gram is 4.18 J/g K.) (a) 20.8 g (b) 26.0 g (c) 117 g (d) 142 g 14. From the values given for ΔH0 and ΔS0 at 298 K, which of the following reactions is spontaneous under standard conditions at 298 K? (a) N2(g) + 3F2(g) → 2NF3(g) ΔH0 = -249 kJ;ΔS0 = -278 J/K (b) N2(g) + 3Cl2(g) → 2NCl3(g) ΔH0 = 460 kJ;ΔS0 = -275 J/K (a) N2F4(g) → 2NF2(g) ΔH0 = 85 kJ;ΔS0 = 198 J/K (a) 2POCl3(g) → 2PCl3(g) + O2(g) ΔH0 = 572 kJ;ΔS0 = 179 J/K 15. According to the band theory, which of the following provides an explanation for the electrical conductivity of metals? (a) A partly filled conduction band (b) A filled valence band (c) A valence band overlapping an empty conduction band (d) A small gap between the valence band and the conduction band Problems: 16. Write the Lewis structures and give the shapes of each of the following molecules; predict which substance of each pair has the higher boiling point with proper explanations: (16%) (a) PF3 or PF5 (b) CO2 or SO2 (c) XeF2 or IF3 (d) cis-CHCl=CHCl or trans-CHCl=CHCl 17. Briefly explain the following substances. What kinds of structure or functional groups are required? Give one application for each of them. (8%) (a) liquid crystal (b) ionic liquid 18. Calculate the ΔE, ΔH, ΔS, ΔG, q, and w values when expanding 0.165 mol of He gas in 0.500 L at 25℃ against an external pressure of 2.50 atm isothermally. (10%) 19. (a) Sketch the 3s molecular orbitals for a linear (Na)6 where all the Na atoms lie on the z axis. Correlate them with the molecular-orbital energy level diagram. (8%) (b) Indicate the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbitals. (2%) (c) What will be the molecular-orbital energy level diagram if the Na tomes in (Na)6 are arranged in a hexagon? (8%) 20. (a) Show the molecular-orbital energy-level diagram of BC, indicating the bonding and anti-bonding orbitals. (5%) (b) Write the valence-shell electron configuration of BC. (2%) (c) What are the bond orders of BC, BC+, and BC-, respectively? Also, put them in the order of increasing bond length. (5%) (d) Which of the above three species are "paramagnetic"? (3%) 21. Fermentation consistent of conversion of fructose (C6H12O6) to ethanol (C2H5OH) and CO2. (a) Is this an exothermic or endothermic process? (b) If you want to keep the fermentation process at a constant temperature, how much water is required for each liter of alcohol produced? Assume that the water starts at 25.0℃ and cannot get warmer than 28.5℃. (10%) (ΔHf of C6H12O6(fructose) = -1265.6 kJ/mol, ΔHf of C2H5OH = -277.6 kJ/mol, ΔHf of CO2 = -393.5 kJ/mol, specific heat of water = 1.00 cal/g-K, density of ehtanol is 0.789 g/mL) 22. A reference book lists the following values for carbon tetrachloride at 298 K. Estimate the normal boiling point of carbon terachloride. (5%) ───────────────────────────────── Substance ΔHf0 (kJ/mol) ΔGf0 (kJ/mol) S0 (J/mol-K) ───────────────────────────────── CCl4(g) -102.9 -60.63 309.7 CCl4(l) -135.4 -65.27 216.2 ───────────────────────────────── Useful informations: gas constant, R = 0.08206 atm L mol-1 K-1 = 8.314 J mol-1 K-1 Avogadro constant NA = 6.022 x 10^23 /mol Planck's constant, h = 6.626 x 10^(-34) J s = 6.626 x 10^(-27) erg s 1 L atm = 101.3 J 1 cal = 4.184 joule --

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