课程名称︰普通化学丙 课程性质：必修 课程教师︰黄信炅 开课系所︰物治系、农艺系 考试日期（年月日）︰100／1／14 考试时限（分钟）：10:20－13:10 (170 分钟) 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 1. Write the most possible Lewis structure and the molecular structure for each of the following: (14 pts) (a) NO2 (b) NO (c)I3^- (d)NO4^3- (e)IF5 (f)XeF2 (g) CH2CL2 2. Nitrous oxide (N2O) has three possible Lewis structures: ‥ ‥ ‥ ‥ N ＝ N ＝ O ←─→ : N ≡ N － O : ←─→ : N － N ≡ O : ‥ ‥ ‥ ‥ Given the following bond lengths, N－N 167 pm N＝N 120 pm N≡N 110 pm N－O 147 pm N＝O 115 pm Rationalize the observation that the N－N bond length in N2O is 112 pm and that the N－O bond length is 119 pm. Can you eliminate any of the resonance structures? Please explain the reasins. (4 pts) 3. The diatomic molecule OH exists in the gas phase. The bond length and bond energy have been measured to be 97.06pm and 24.7 kJ/mol, respectively. Assume that the OH molecule is analogous to the HF molecule and that the MOs result from the overlap of a pz orbital from oxygen andd the 1s orbital of hydrogen (the O－H bond lies along the z axis) a. Draw pictures of the sigma bonding and antibonding molecular orbitals in OH. (2 pts) b. Which of the two MOs has the greater hydrogen 1s character? (2 pts) c. Can the 2px orbital of oxygen form MOs with the 1s orbital of hydrogen? (2 pts) d. Estimate the bond order for OH and OH^+. (2 pts) 4. Draw a molecular orbital diagram for O2 and N2. Using molecular orbital theory, explain why the removal of one electron in O2 strengthens bonding, while the removal of one electron in N2 weakens bonding. (6 pts) 5. Consider the following data for xenon: Triple point: -121。C, 280 torr Normal boiling point: -112 。C Normal melting point: -107 。C Which is more dense. Xe(s), or Xe(l)? How do the melting point and boiling point of xenon depend on pressure? Please estimate the heat of vaporization for xenon as possible as you can. (Please explain the reasons) (8 pts) 6. Consider the hypothetical reaction A + B + 2C → 2D + E Where the rate law is Rate = -Δ[A]/Δt = k[A][B]^2[C]^3 An experiment is carried out where [A]0 = 1.0 x 10^=2 M, [B]0 = 3.0 M and [C]0 = 2.0 M. The reaction is started, and after 8.0 seconds, the concentration of A is 3.8 x 10^-3 M. a. Calculate k for this reaction. (2 pts) b. Calculate the half-life for this experiment. (2 pts) c. Calculate the concentration of A after 13.0 seconds. (2 pts) d. Calculate the concentration of C after 13.0 seconds. (2 pts) 7. Given this data from a study on how the rate of a reaction was affected by the concentration of the reactants Experiment [A] [B] [C] Initial rate (mol L^-1 hr^-1) 1 0.200 0.100 0.600 5.0 2 0.200 0.400 0.400 80.0 3 0.600 0.100 0.200 15.0 4 0.200 0.100 0.200 5.0 5 0.200 0.200 0.400 20.0 Please determine the rate law and the rate constant for this reaction. (4 pts) 8. Phosphorus (V) chloride, PCl5, dissociates on heating to give phosphorus (III) chloride, PCl3, and chlorine. PCl5(g) ←→ PCl3(g) + Cl2(g) A closed 2.00-L vessel initially contains 0.0100 mol PCl5. What is the total pressure at 250。C where equilibrium is achieved? The value of Kc at 250。C is 4.15 x 10^-2. (4 pts) 9. Arrange the following 0.10 M solutions from lowest to highest pH: NaF, NaC2H3O2, C5H5NHCl, KOH, HCN. (Ka for HCN is 6.2 x 10^-10; Ka for HF is 7.2 x 10^-4; Ka for HC2H3O2 is 1.8 x 10^-5; and Kb for C5H5N is 1.7 x 10^-9) (4 pts) a) HCN, C5H5NHCl, NaF, NaC2H3O2, KOH b) C5H5NHCl, HCN, NaF, NaC2H3O2, KOH c) NaF, NaC2H3O2, HCN, C5H5NHCl, KOH d) KOH, NaC2H3O2, NaF, HCN, C5H5NHCl e) none of these 10. What will happen to the number of moles of SO3 in equilibrium with SO2 and O2 in the decomposition reaction of SO3, ΔH。 = 197 kJ, in each of the following cases? (8 pts) a) Oxygen gas is added. b) The pressure is decreased by increasing the volume. c) The pressure is increased by adding argon gas. d) The temperature is increased. 11. Consider the titration of 100.0 mL of 0.100 M H2NNH2 (Kb = 3.0 x 10^6) with 0.200 M HNO3. Calculate the pH of the resulting solution after each of the following volumes of HNO3 has been added. (10 pts) a. 0.0 mL b. 20.0 mL c. 25.0 mL d. 50 mL f. 100.0 mL 12. Prove that for a gaseous reation, ΔG = ΔG。+ RTlnQ where Q is the reaction quotient, Π(Pproducts)^np Q = ───────── Π(Preactants)^nr (8 pts) 13. Which of the follwing mixtures would result in buffered solutions when equal volumes of the two solutions are mixed? Please estimate the pH values for these solutions. (a) 0.1 M KOH and 0.1 M CH3NH3Cl (b) 0.5 M NH3 and 0.25 M NH4Cl (c) 0.2 M HNO3 and 0.4 M KNO3 (d) 0.1 M KOH and 0.2 M CH3NH3Cl (e)0.2 M HCl and 0.4 M HF (f) 0.1 M HNO3 and 0.2 M NaF (g) 0.2 M HCl and 0.4 M NaOH (h) 0.2 M CH3COOH and 0.1 M NaOH (i) 0.1 M HCl and 0.15 M CH3COONa. (Kb for CH3NH2 is 4.38 x 10^-4, Kb for NH3 is 1.8 x 10^-5, Ka for CH3COOH is 1.8 x 10^-5 and Ka for HF is 7.2 x 10^-4) (18 pts) 14. The standard free energies of formation and the standard enthalpies of formation at 298 K for difluoroacetylene (C2F2) and hexafluorobenzene (C6F6) are ΔG。f (kJ/mol) ΔH。f (kJ/mol) C2F2 191.2 241.3 C6F6 78.2 132.8 For the following reaction: C6F6(g) ←→ 3C2F2(g) Caculate ΔS。 and K at 298K. If ΔH and ΔS do not depend on temperature, please calculate K at 3000 K. (6 pts) --

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