课程名称︰普通化学甲上 课程教师︰苏志明 课程性质︰必带 开课学院：生农学院 开课系所︰农业化学系 考试日期（年月日）︰2011/1/14 考试时限（分钟）：10:20~12:30 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 1.The following figure indicates three types of eletrostatic interactions between molecules and/or ions. Assuming that the intermolecular distance R is much larger than the intramolecular charge separation d, derive the fuctional forms of the intermolecular potential of the three electric charge distribution.(Note: the final forms should be expressed in terms of the dipole moment and R for the charge-dipole and dipole-dipole interactions ,and each + or - sign indicates a positive or negative charge. You could denote the the related constant in the Coulomb potential as k.) _____________________ charge-charge 。 R 。 q+ q- _____________________ charge-dipole 。 R 。 。 q+ δ+ δ- ______ d _________________________ dipole-dipole 。 。 R 。 。 δ+ δ- δ+ δ- ______ ______ d d 2.(a)In constructing the molecular orbitals of homo-nuclear diatomic molecules, such as N2, O2, ...etc, one obtains the so-called σ, σ^*, π, and π^* molecular ornitals . Explain these orbitals in terms of their shapes and spatial symmetry. (b)One knows that the energy orderings of the above molecular orbitals are σ(2s) < σ^*(2s) < π(2p) < σ(2p) < π^*(2s) < σ^*(2s) for Li,Be,B,C,and N and σ(2s) < σ^*(2s) < σ(2p) < π(2p) < π^*(2s) < σ^*(2s) for O,F,and Ne. + - Gives the elevronic configurations and their bond orders of Li2,Be2,C2,C2,O2, and F2 homo-nuclear diatomic systems. (c)Explain why liquid oxygen is a paramagnetic material. 3.Construct the molecular orbitals of the hetero-nuclear molecule HF. Explain the nature of chemical bonding of HF, and the origin of the eletric dipole moment of HF in terms of the approximate molecular wave fuction obtained. Note that the first ionizaton energy of the F atom is much higher than that of the H atom. 4.The vapor pressure of a substance follows the Clausius-Clapeyron equation -△Hvap lnP = -------- + C RT (a)Derive the following relationship between the pressure P1 and P2, and the absolute temperatures at which they are measured, T1 and T2. P1 -△Hvap 1 1 ln---- = --------- (---- - ----- ) P2 R T1 T2 (b)Gasoline is a mixture of hydrocarbons, a major component of which is octane C8H18. Octane has a vapor pressure of 13.95 torr at 25℃ and a vapor pressure of 144.78 torr at 75℃.Calculate the heat of vaporation of octane. (c)Calculate the normal boiling point of octane. (d)Calculate the vapor pressure of octane at -30℃. 5.(a)At molecular level, what factor is responisible for the steady increase in viscosity with increasing molecular weight in the hydrocarbon series from n-hexane to n-nonane (i.e. all are in straight chains). (b)Although the viscosity varies over a factor of more than two in the above alkane series, the surface tension at 25℃ increases by only about 20% in the same series. How do you account for this? (c)n-Octyl alcohol, CH3(CH2)7OH, has a viscosity of 1.01x10^-2 kg/ms,much higher than n-nonane (C9H20), which has about the same molecular weight.What account for this difference? 6.Consider the molecule PF4Cl. (a)Draw a Lewis structure for the molecule, and predict its electron-domain geometry (i.e.only consider the electron-pairs of the molecule). (b)Which would you predict to take up more space, a P-F bond or a P-Cl bond? Explain. (c)Predict the molecular geometry of PF4Cl. How did you answer for part (b) influence your answer in part (c)? (d)Would you expect the molecule to distort from its ideal molecular geometry ?If so, how would it distort? 7.The molecule 2-butene, C4H8, can undergo a geometric change called cis-trans isomerization. (a)What is the hybridization at the two central carbon atoms of 2-butene? (b)The isomerization occurs by rotation about the central carbon-carbon bond. Explain why the π bond between the two central carbon atoms is destroyed halfway through the ration from cis- to trans-2-butene. (c)Based on average bond enthalpies, how much energy per molecule must be supplied to break the C-C π bond? (d)What is the longest wavelength of light that will provide photons of sufficient energy to break the C-C π bond and cause the isomerization? 8.The stucture of two typical explosives are shown as follows: H H H 　 | | | H─C─────C─────C─H | | | O O O | | | N N N ╱ ╲ ╱ ╲ ╱ ╲ O O O O O O Nitroglycerin TNT (a)Use bond enthalpies to estimate the enthalpy change for the explosion of 1.00 g of nitriglycerin. (b)Write the balanced equation for the decomposition of TNT in the absence of any other substance, such as oxygen. Assume that, upon explosion, TNT decomposes into N2(g), CO2(g),H2O(g),and C(s). 9.For 1 mole of real gas,the van der Waals equation is expressed as a (P+-----)(V-b) = RT V^2 The a and b constants of H2 are 0.244 (L^2-atm/mol^2) and 0.0266 (L/mol), and 1.39 and0.0391, respectively. With regard to the following figures of PV/RT vs. P behaviors and starting from the van der Waals equation, answer the following questions: (a)Explain why in the PV/RT vs. P curves, the N2 gas shows a negative slope while the H2 is positive in the low pressure regime at 298K. (b)Explain why at 1000K, the PV/RT vs. P curve becomes positive with respect to the ideal gas? Figure 10.23 and Figure 10.24 are shown in page10. http://www.teachersites.net/content/4/92/1047/my%20files/Unit%204%20Gases.pdf --

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