五、（15分）
1. 已知0.025 mol·dm–3的一元弱酸水溶液的凝固点为–0.060℃，试计算该酸的pKa。（已
知Kf,H2O =1.86）
2. 试计算0.100 M的难挥发的非电解质水溶液在75℃的蒸气压。
（已知ΔvapHm = 40.67 kJ ·mol–1） 3. 某稀溶液1kg溶剂中，含溶质B的物质的量为m摩尔，其沸点升高常数为Kb，若
溶质按2B B2在溶液中缔合，其平衡常数为K，试证明K = 2 。
Kb(mKb- Tb)(2 Tb-mKb)在证明过程中，应用了什么假设？等式左侧的K是经验平衡常数还是热力学平衡常数？
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Additional Exam (20 points)
1. Each of the questions or incomplete statements below is followed by four suggested
answers or completions. Please give your answer that is best in each case.
(1) Which of the following sets of conditions describes a system undergoing a reversible
change? ( ) ?Ssystem ?Ssurronding ?Stotal
(A) positive zero positive (B) positive negative zero (C) positive positive zero (D) negative zero negative
(2) The statement that heat cannot spontaneously flow from a colder to a hotter body is a
resulf of ( ) (A) the first law of thermodynamics (B) the second law of thermodynamics (C) the third law of thermodynamics (D) Le Chatelier’s principle
(3) Which of the following factors influences the value of Ka for the dissociation of
formic acid? ( ) (A) temperature (B) pressure (C) pH (D) the initial concentration of HCO2H (4) In a saturated solution of iodine in chloroform, the mole fraction of iodine is 0.0147,
what is the total vapor pressure of such a saturated solution? ( p I2 = 0.31 torr, p CHCl 3=199.1 torr, all apply at 25℃) ( ) (A) 0.31torr (B) 196.5torr (C) 199.1torr (D) 196.2torr
(5) Which of the following is not a Lewis base ? ( )
(A) NH4+ (B) OH– (C) O2 (D) SCN–
(6) Which of the following is not a conjugate acid―base pair? ( )
(A) NH4+/NH3 (B) H2O/OH– (C) H3O+/H2O (D) CH4/CH3– (7) Which of the following statements is always true for an ideal gas? ( )
(A) If the temperature and volume of a gas increase at constant pressure, the amount
of gas must also increase.
(B) If the pressure increases and the temperature decreases for a constant amount of
gas, the volume must decrease.
(C) If the volume and the amount of gas both decreases at constant temperature, the
pressure must decrease. (D) None of above all.
(8) Increasing the temperatures of a liquid will do which of the following? ( )
(A) Increase its boiling point (B) Increase its melting point (C) Increase its vapor pressure (D) All of the above
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(9) A 0.100 mol·dm–3 solution of sulfuric acid in water freezes at –0.371 ℃. Which of the
following statements is consistent with this observation? (Kf =1.86) ( ) (A) H2SO4 does not dissociate in water.
(B) H2SO4 dissociates into H3O+ and HSO4– ions in water.
(C) H2SO4 dissociates in water to form two H3O+ ions and one SO42– ion. (D) H2SO4 associates in water to form (H2SO4)2 molecules.
(10) For which of the following reactions change roughly equivalent changes in internal
energy and enthalpy ( )
(A) 2H2(g) + O2(g) 2H2O(g)
(B) Pb(NO3)2(s) + 2KI(s) PbI2(s) + 2KNO3(s)
(C) CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) (D) NaOH(s) + CO2(g) NaHCO3(s)
2. The phase diagram is a convenient way to indicate the phases of a substance as a function of temperature and pressure. Answer the following questions based on the phase diagram of water given below:
(1) What phases are present at A, B, C, and D? (2) Why does ice not sink in its own liquid?
(3) When water freezes, it expands. Explain
this observation using the Clausius― Clapeyron equation, which may be expressed
by
dp?H. Here, ΔH and ΔV denote ?dTT?Vthe change of molar enthalpy and molar volume of water, respectively.
(4) A glass container partially filled with water
is connected to a vacuum pump. What changes will be observed when the pump is turned on for a long time? Please explain by using the phase diagram of water.
(5) A man is skating on the surface of a sheet of ice where the air pressure is 1 atm and the
temperature is 0 C. What changes will be observed along the skating track on the surface of the ice, assuming the ice can withstand his weight without cracking?
o
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