Entropy of a sealed room with an open-door refrigerator

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Homework Help Overview

The discussion revolves around the entropy changes in a sealed room containing a working refrigerator with its door open. Participants are examining the thermodynamic implications of this setup, particularly focusing on the heat exchange processes and the definition of entropy in relation to the system's energy dynamics.

Discussion Character

  • Conceptual clarification, Assumption checking, Exploratory

Approaches and Questions Raised

  • Participants are exploring the implications of the refrigerator's operation within a sealed environment, questioning the assumptions about heat transfer and energy exchange. There are discussions about whether the system's internal energy is increasing and the role of work done on the system.

Discussion Status

The conversation is ongoing, with participants providing insights and prompting further examination of the original poster's reasoning. Some guidance has been offered regarding the need to consider the entire system rather than focusing solely on the refrigerator's internal processes.

Contextual Notes

There is a mention of a mark scheme indicating that entropy increases, which has prompted the original poster to seek clarification on their understanding. The discussion also touches on the nature of the refrigerator's operation and the assumptions about the sealed room's insulation.

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Homework Statement
A working refrigerator with the door open is placed in a sealed room.

What change occurs to the entropy of the room?
Relevant Equations
Q= ΔU + W
dS = dQ / T
A working refrigerator with the door open is placed in a sealed room.
The entropy of the room
A. is zero.
B. decreases.
C. remains unchanged.
D. increases.

I chose C.
Here's my thought process:
In a working refrigerator, a compressor compresses a refrigerant (at a gas state) in the coil, and the refrigerant turns into liquid. The latent heat of condensation is rejected into the room, making room hotter. When the refrigerant travels into the refrigerator, an expansion valve expands the refrigerant and converts it into gas. The latent heat of fusion comes from the interior of the refrigerator, which causes the inside to become cooler. However, in this case, the door is open. This means that the net heat exchange is 0 as latent heat of condensation = latent heat of fusion.

In my knoweldge, the compression and expansion processes are adiabatic, so there is no heat transferred to or from the system.

But the mark scheme says the entropy increases. Can you explain which part of my solution is wrong and why?
 
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Is it plugged in?
 
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it says 'working'
 
techsingularity2042 said:
it says 'working'
Right, so think about the energy.
 
techsingularity2042 said:
it says 'working'
What @haruspex is saying is that you've gotten lost in the details. Take as your system the combination of room (assumed insulated) and refrigerator. Is work being done on that system? Is the internal energy of that system increasing?
 
techsingularity2042 said:
In my knowledge, the compression and expansion processes are adiabatic, so there is no heat transferred to or from the system.

But the mark scheme says the entropy increases. Can you explain which part of my solution is wrong and why?
What energizes the compression process, which must overcome the friction resistance of the tubes-condenser-evaporator to circulate through the system and to go through the expansion orifice or valve?
It seems to me that the "sealed room" is still being penetrated by some kind of external energy.

Fig.-6-6_revised-768x630.png
 

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