課程名稱︰材料熱力學
課程性質︰必帶
課程教師︰林招松
開課學院：工學院
開課系所︰材料系
考試日期（年月日）︰102.10.18
考試時限（分鐘）：180分鐘
是否需發放獎勵金：是
（如未明確表示，則不予發放）
試題 :
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(
巨觀狀態) 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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