A pistonandcylinder device with a freefloating piston contains saturated water vapor at 225^{o}C. Heat is
lost from the water to the surroundings which are at 25^{o}C. 

Eventually, all of the water has condensed and the cylinder contains saturated liquid water
at 225^{o}C. Is this process internally reversible? Reversible? Irreversible? Explain your answer. 





Read : 
What can be said about
this case of heat transfer process for (a) isothermal cooling of the water and (b) contact between 225^{o}C and 25^{o}C surroundings? 


Given: 
T_{w} 
225 
^{o}C 

Find: 
Internally Reversible
? 
Reversible ? 


T_{surr} 
25 
^{o}C 

Explain. 


Diagram: 













Assumptions: 
1  
The system is the water in the pistonandcylinder assembly. 



2  
The system undergoes a constanttemperature process from saturated vapor to saturated liquid. 












Equations
/ Data / Solve: 




















No equations
are needed to resolve this problem. 













There are no equations to solve. 












Verify: 
None of the
assumptions made can be verified with the given information. 












Answers : 
Since the temperature is constant during the process, the pressure also remains constant. As shown by the
TV Diagram, the
process is a sequence
of equilibrium states,
and thus is internally reversible. 













The process is
not reversible because there is a
significant irreversibility in the surroundings. The spontaneous heat transfer taking
place between the water at 225^{o}C and the surroundings at 25^{o}C is irreversible. 










































































