
Concept explainers
The change in enthalpy
The change in entropy
The change in enthalpy
The change in entropy

Answer to Problem 71P
The change in enthalpy
The change in entropy
The change in enthalpy
The change in entropy
Explanation of Solution
Write the mean change in enthalpy
Here, enthalpy of water vapor at temperature of 647.1 K is
Write the change in enthalpy
Here, molar mass of water vapor is
Write the mean change in entropy
Here, gas constant is R, initial pressure is
Write the change in entropy
Write the reduced temperature
Here, critical temperature is
Write the reduced pressure
Here, critical pressure is
Write the reduced temperature
Here, critical temperature is
Write the reduced pressure
Here, critical pressure is
Write the change in enthalpy
Here, change in enthalpy of water vapor is
Write the change in enthalpy
Here, change in entropy of water vapor is
Conclusion:
Convert the unit of initial temperature
Convert the unit of initial temperature
Refer table A-23, “Ideal gas properties of water vapor”, obtain the enthalpy of water vapor at temperature of
Substitute
Refer table A-1, “Molar mass properties table”, obtain the molar mass
Refer the table A-20,”Water vapor properties of water vapor table”, select the entropy of water vapor at temperature of
Substitute
Substitute 873 K for
Substitute
Refer the table A-15, “Nelson-Obert generalized compressibility chart”, select the initial state of compressibility factor
Substitute 673 K for
Substitute
Refer the table A-15, “Nelson-Obert generalized compressibility chart”, select the initial state of compressibility factor
From the gas constant properties table A-1, select the gas constant of water vapor as
Substitute
Substitute
Thus, the change in enthalpy
Substitute
Substitute
Thus, the change in entropy
Refer table A-6, “Superheated water table”, select the inlet enthalpy and exit enthalpy at pressure of
Thus, the change in enthalpy
Refer table A-6, “Superheated water table”, select the inlet entropy and exit entropy at pressure of
Thus, the change in entropy
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Chapter 12 Solutions
Thermodynamics: An Engineering Approach
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