20. For a steam engine, steam enters at 500°C and is exhausted at 120°C. What is the maximum efficiency of this engine? (A)0.63 (B)0.55 (C)0.49 (D)0.75 (E)0.33

8. About ideal gas, (A)An ideal gas is an assemblage of volumeless noninteracting particles which obeys the ideal gas law, PV = RT. (B)The internal energy of an ideal gas arises solely from the translational motions of the gas particles and hence is a function only of temperature, (C)The enthalpy of an ideal gas is a function only of temperature, (D)The internal energy U is constant with respect to the gas volume, i.e. (dU/dV)T = 0, hence the pressure P can be expressed as P = (dS/dV)T, (E)The above are all correct.

20. For a steam engine, steam enters at 500°C and is exhausted at 120°C. What is the maximum efficiency of this engine?

(A)0.63

(B)0.55

(C)0.49

(D)0.75

(E)0.33

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