课程名称︰材料热力学一 课程性质︰必带 课程教师︰林招松 开课学院：工学院 开课系所︰材料系 考试日期（年月日）︰102.10.18 考试时限（分钟）：180分钟 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : Gas constant R = 8.3144J/(mole K) = 1.987 cal/(mole K) = 0.082057 (liter-atm)/ (mole K). Note cv of a monoatomic ideal gas is equal to 1.5 R, and is independent of temperature. 1. A system is subjected to a series of processes, as shown in Figure 1. When the system is taken from state a to state b along the path acb, 800 J of heat flow into the system, and the syatem does 300 J of work. (15%) (1) Suppose that the system is taken from a to b along the path adb. How much heat flow into the system given that the work done by the system is 120 J ? (2) Suppose that the system is returned from state b to state a directly. The work done on the system is 220 J. Does the system absorb or liberate heat during the return ? How much ? P| | | c_________b | | .| | | . | | | . | | | . | | | . | | | . | | a|,______|d | _________________ V Figure 1 2. An ideal gas (one mole) initially at pressure P1, volume V1, and temperature T1 can expand reversibly either by an isothermal or by an adiabatic process to a final volume of V2. (15%) (1) Which of the two modes of expansion delivers the largest amount of useful work ? (2) Derive the ratio of the work done by the isothermal process to the work done by the adiabatic process. Hint: express the answer in terms of R, T1, V1, V2, P1. Note that cv the ideal gas is equal to 1.5 R. 3.One mole of a monoatomic ideal gas is subjected to the folloeing sequence of steps. (i) Starting at 400 K and 5 atm, the gas expands isothermally and freely into a vacuum to triple its volume. (ii) The gas is next heated reversibly to 500 K at constant volume. (iii) The gas is reversibly expanded at constant temperature until its volume is again tripled. (iv) The gas is Finally reversibly cooled to 400 K at constant pressure. Calculate the work done, the heat absorbed, and the change in internal energy, enthalpy, and entropy. (20%) 4. Derive the following expression for an ideal gas (15%) (1) cp - cv = R (2) the efficiency of the Carnot cycle is 1-T(low)/T(high) 5. About the second of thermodynamics (15%) (1) What is the usefulness of the second law of thermodynamics ? (2) Give five examples of the operation of the second law of thermodynamics in your daily experience. 6. Comment on the correctness of the statement of each question. Ansxer "four" out of the following six questions. (20%) (1) During an irreversible process, 22 kJ of energy is removed as heat from a thermodynamic system at constant temperature. The entropy change of the system can be positive. (2) In any process in which a thermally isolated system goes from one macrostate( 巨观状态) to another macrostate, the entropy change of the system is equal to zero. (3) Work done in a free expansion process is maximum. (4) The infinitesimal quantity dF = (x^2-y)dx + xdy is an exact differential. (5) An isentropic process is always reversible and adiabatic. (6) In a reversible cycle, the entropy of the system does not change. --

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