A vertical piston-cylinder device contains water and is being heated on top of a range. During the process, 63 Btu of heat is transferred to the water, and heat losses from the side walls amount to 8 Btu. The piston rises as a result of evaporation, and 5 Btu of work is done by the vapor. Determine the change in the energy of the water for this process
The water would have a change in the energy of 50 BTU
Explanation:
Under the assumption that the piston-cylinder system is a closed system, then the conservation law of the system would be: [tex]E_{in}-E_{out}=E_{change}[/tex], where [tex]E_{in}[/tex] is all the energy that goes into the system, [tex]E_{out}[/tex] is all the energy that leaves the system and, [tex]E_{change}[/tex] is the change of the energy of the system.
For this case the energy that is feeded to the system is heat: 63 BTU.
There is two ways that energy is leaving this system: 8 BTU of heat as losses through the side walls and, 5 BTU of work done by the vapor on the piston.
Then the change of energy of the system is: [tex]E_{change}=E_{in}-E_{out}=63 BTU-(8BTU+5BTU)=50BTU[/tex].
