Understanding Work and Energy Transfers in Gas Processes

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Homework Help Overview

The discussion revolves around understanding the concepts of work and energy transfers in gas processes, specifically focusing on the relationship between internal energy, heat transfer, and work done by or on the gas.

Discussion Character

  • Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants are exploring the relationship between heat transfer, work done, and changes in internal energy. There is confusion regarding the signs of work and heat, particularly in distinguishing between work done on the gas versus work done by the gas.

Discussion Status

Some participants have provided hints and attempted to clarify the definitions of work in relation to energy transfers. There is ongoing exploration of how to correctly apply the equations related to energy changes, but no consensus has been reached on the correct interpretation or calculation.

Contextual Notes

Participants note potential ambiguities in textbook definitions of work, which may contribute to confusion. The discussion includes a focus on the signs of energy transfers and the implications for calculating work done in gas processes.

lando45
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If the change in internal energy of a gas during a process is 1500 J and the heat transferred to the gas during the process -400 J, what is the work done by the gas?

I immediately though the answer to this question was 1100J, but it's not, I am completely confused by this. How can it not be 1100?
 
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Q(in) + W(in) = DeltaE

Q(in) is NEGATIVE , but DeltaE is POSITIVE.

so, what's W(in)?

Now notice that they're asking for W(out) ...
 
Q(in) + W(in) = DeltaE
-400 + W(in) = 1500
W(in) = 1900

So now how do I find W(out)? I figured that [W(in) + W(out)]/2 = change in internal energy which is how I came up with my original answer of 1100J, but that's incorrect.
 
Last edited:
HINT: W(out) is the opposite to W(in)
 
Work transfers Energy OUT of one object and INto another ...
I was referring to Work that transfers Energy Into the gas as W(in).
Energy is conserved, so that W(in) would be W(out) for some other object.

Textbooks are notoriously flaky about which W they mean.
I envision all Energy transfers going into my sample, which raises its T.
 

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