A vertical piston–cylinder device contains water and is being heated on top of a range. During the process, 73 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.

60 btu

Explanation:

given:

solution:

the total change in the system energy can be calculated as follows

ΔE=

    =73-5-8

    =60 btu

note :

work is done by the system so it has a negative sign

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