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Question: an ideal gas with cp 72r and cv ...

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An ideal gas with Cp = (7/2)R and Cv = (5/2)R undergoes the following reversible
changes in a series of nonflow processes:


a. From an initial state of 70(°F) and 15(psia), it is compressed adiabatically to 75(psia).
b. It is then cooled to 70(°F) at a constant pressure of 75(psia).
c. Finally, the gas is expanded isothermally to its original state.


Calculate Q, WEC, ΔU, and ΔH for each of the three processes and for the entire cycle. Next,
calculate Q, WEC, ΔU, and ΔH for exactly the same changes in state that you computed above for
(a)-(c), but now assuming that each process is irreversible with an efficiency of 75 percent
compared to reversible operation. Specifically, if the reversible process produces 10 BTU of
work, the irreversible process should produce 0.75(10)=7.5 BTU, and if the reversible process
requires BTU kJ of work, the irreversible process should require 10/0.75 = 13.33 BTU. Use the
exact same initial and final states you already computed (this will require nonzero heat flow in
part (a)).

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