课程名称︰物理化学一─热力学 课程性质︰必修 课程教师︰陆骏逸 开课学院：理学院 开课系所︰化学系 考试日期（年月日）︰2013/01/11 考试时限（分钟）：130 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 1.Boltzmann said that S = k_B ln(Ω), whereas Gibbs' entropy says S = -k_B ΣP_i ln(P_i) where P_i indicates the apperaing probability of the microstate i. Explain when do you use the former and when to use the latter. 2.On the top of Jade mountain, the pressure is only 0.6 atm. Estimate the boiling point there. The heat of vaporization is 41kJ/mol. 3.When you boil a liquid on an oven, often the boiling bubbles start to appear at a temperatiure which is slightly higher than the reported boiling. In terms of the Laplace pressure, explain the discrepancy. 4.Suppose tha a non-ideal gas obeys the van der Waals equation of state _ _ (P+a/V^2)(V-b) = RT. Microscopically the potential energy between two gas molecules isapproximated as the following form: V(r) ┴ │ │ │ │ │ │ │ 1│ 2 3 ├─┼──────────├ │ │ │ r(Å) -0.1eV ┼ │ ┌─┘ │ │ │ -0.2eV ┼ └─┘ │ (a)Calculate the constant a and b. (b)Estimate the location (T_c,P_c) of the gas/liquid critical point. 5.Consider a string of atoms which form one dimensional lattice. The molecular mass is 100 g/mol.The distance between the neighboring atoms is 2Å, and the potential between the neighboring atoms can be described by Hookian spring with a spring constant k_s = 100eV/nm^2. The longitudinal vibrations of these atoms form the sound wave. Ignore the transverse vibrations in this exam question. (a)Plot the vibration frequency as the function of the (1d) wave vector k = 2π/wavelength. (b)How does the heat capacity of this system change with the temperature at low temperature? Explain your reasoning. (c)Estimate the characteristic (Debye) temperature for this system. (Above this characteristic temperature, the heat capacity will be roughly a constant.) 6.Einstein's solid model predicts a heat capacity which does not depend on the dimensionality of the solid. The heat capacity of the Debye's solid model, however, depends strongly on the dimensionality of the solid. Explain the main reason which makes the difference. 7.Suppose that you have an equilibrium crystal, whose shape obeys the Wulff construction rule. The cross section of the crystal has the following shape, where L1:L2:L3=2:√2:1. All the angles are 3π/4. Suppose that the surface energy γ1 = 1J/m^2. What are the values for γ2 and γ3? γ1 /──────\ γ2 / L1 L2 \ │ │ │ L3 │ γ3 \ / \──────/ --

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