Question

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

Answer 1

Answer:

The water would have a change in the energy of 50 BTU

Explanation:

1. Under the assumption that the piston-cylinder system is a closed system, then the conservation law of the system would be: $E_{in}-E_{out}=E_{change}$, where $E_{in}$ is all the energy that goes into the system, $E_{out}$ is all the energy that leaves the system and, $E_{change}$ is the change of the energy of the system.
2. For this case the energy that is feeded to the system is heat: 63 BTU.
3. 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.
4. Then the change of energy of the system is: $E_{change}=E_{in}-E_{out}=63 BTU-(8BTU+5BTU)=50BTU$.