课程名称︰普通化学乙下 课程性质︰系内必带 课程教师︰金必耀 开课学院：工学院 开课系所︰土木工程学系 考试日期（年月日）︰99/6/25 考试时限（分钟）：130min 是否需发放奖励金：是，谢谢 （如未明确表示，则不予发放） 试题 : 1.(6%) Consider the ammonia synthesis reaction N2(g) + 3H2(g) --> 2NH3(g), where ΔG°= -33.3KJ per mol of N2 consumed at 25℃. For each of the following mixtures and products at 25℃, predict the direction in which the system will shift to equilibrium. a. PNH3=1.00 atm, PN2=1.47 atm , PH2=1.00*10^-2 atm b. PNH3=1.00 atm, PN2=1.00 atm , PH2=1.00 atm 2.(5%) The overall reaction for the corrosion (rusting) of iron by oxygen is 4Fe(s) + 3O2(g) --> 2Fe2O3(s), calculate the equilibrium constant for the reaction at 25℃ using the following data. | Substance | ΔH°f(kJ/mol) | S°(J/mol-K) | | Fe2O3(s) | -826 | 90 | | Fe(s) | 0 | 27 | | O2(g) | 0 | 205 | 3.(4%) Simply describe Le Chatelier's principle and how to predict qualitatively the charge or shift of the equilibrium constant as the temperature of the endothermic or exothermic reaction changes.(hint: you should interpret in words and illustration.) 4.(4%) Show and shortly derive van't Hoff equation. Is there the similar tendency between van't Hoff equation and Le Chatelier's principle. 5.(8%) Benzene has a melting point of 5.5℃ and the enthalpy of fusion of 10.04kJ/mol. The molar heat capacities at constant pressure for solid and liquid benzene are 100 and 133 J/mol-K, repectively. For the reaction: C6H6(l) <---> C6H6(s), calculate ΔS(sys) and ΔS(surr) at 11.0℃ at constant pressure. 6.(6%) Consider the system: A(g) <---> B(g) at 25℃. a. Assuming that G°(A) = 8996 J/mol and G°(B) = 11718 J/mol, calculate equilibrium constant. b. Calculate the equilibrium pressure that result if 1.00 mol A gas at 1.00 atm and 1.00mol Bgas at 1.00 atm are mixed at 25℃. 7.(7%) A quantitative measure of how efficiently spheres pack into unit cells is called packing efficiency, which is the percentage of the cell space occupied by the sphere. Calculate the packing efficiencies of a simple cubic cell, a body-centered cubic cell, and a face-centered cubic cell.(Hint: the volume of a sphere is 4πr^3/3, where r is the radius of the sphere.) 8.(7%) Briefly describe the difference among insulator, semiconductor, and conductor using the energy band picture? State whether silicon would form n-type or p-type semiconductors with the following element: Ga, Al, As. 9.(7%) The properies of crystalline solids are determined largely by intermolecular interactions. Explain why diamond is harder than graphite. Why is graphite an eletrical conductor but diamond is not? 10.(9%) Given the phase diagram of carbon shown below, answer the following questions: a. How many triple points are there and what are the phases that can coexist at each triple point? b. Which has a higher density, graphite or diamond? c. Synthetic diamond can be made from graphite. Based on the phase diagram, how would you do this? 11.(8%) The following diagram shows the variation of the equilibrium constant with temperature for the reaction: I2(g) <---> 2I(g). Calculate ΔG°, ΔH° , and ΔS° for the reaction at 872K. 12.(6%) Show that the half-time of a second-order reaction is given by t(1/2)= 1/k[X](0). In what fundamental way does the half-life of a second-order reaction differ from a first-order reaction? 13.(6%) The reaction 2N2O5(g) --> 4NO2(g) + O2(g) was studied at several temperatures and the following values of k were obtained. Calculate the value of Ea for this reaction. | T(℃) | 20 | 30 | 40 | 50 | 60 | | k(s^-1) | 2.0*10^-5 | 7.3*10^-5 | 2.7*10^-4 | 9.1*10^-4 | 2.9*10^-3 | 14.(9%) The chart show the relationship of reaction pathway and free energy (kJ/mol) at 300K. a. What is the intermediate? What will it happen if catalyst adds? What does D and E stand for? A --> C is exo- or endothermic reaction? What is the rate-determining step? b. Calculate the ΔG° and K for the overall reaction. c. Set the two differences of energy between A to D and B to E as the activation energies of each. Calculate the rate constant of the overall reaction.(Arrhenius factor of the reaction is 2.11*10^-5 s^-1) 15.(8%) The reaction 2NO + O2 --> 2NO2 exhibits the rate law: Rate=k[NO]^2[O2]. Which of the following mechanism is consistent with this rate law? a. NO + O2 --> NO2 + O slow O + NO --> NO2 fast b. NO + O2 <--> NO3 fast equilibrium NO3 + NO --> 2NO2 slow c. 2NO --> N2O2 slow N2O2 + O2 --> 2N2O4 fast N2O4 --> 2NO2 fast d. 2NO <--> N2O2 fast equilibrium N2O2 --> NO2 + O2 O + NO --> NO2 fast --

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