Calculating Heat Over a Cycle: Q, dU, W

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Homework Help Overview

The discussion revolves around calculating heat transfer over a thermodynamic cycle, specifically focusing on the heat added and expelled during various processes within the cycle. The subject area includes concepts from thermodynamics, particularly the first law of thermodynamics.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to understand when heat is added during the cycle and whether it occurs only in certain processes. They question the application of the equation Q = dU + W for calculating heat transfer. Other participants suggest using this equation for each path segment and inquire about the relationship between temperature and heat flow in specific processes.

Discussion Status

The discussion is ongoing, with some participants providing guidance on the use of the first law of thermodynamics. There are multiple interpretations being explored regarding the heat flow and temperature relationships, indicating a productive exchange of ideas without a clear consensus yet.

Contextual Notes

Participants are navigating the complexities of the thermodynamic cycle and the implications of the first law, with some uncertainty about the definitions and calculations involved. The original poster expresses confusion, indicating a need for clarification on the concepts discussed.

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Homework Statement



How much heat is added over this cycle? During which processes?
What is the heat expelled from d to a?

Homework Equations



http://img838.imageshack.us/img838/6270/29494670.png
(Goes clockwise, abcda)

The Attempt at a Solution



I'm just generally confused overall about this question. Is heat added in the processes which are going "forward"? So would heat only be added during processes a-b and b-c?

And would I use Q = dU + W to calculate the heat added for the processes?

For the 2nd question, for heat expelled, would I still just use Q = dU + W to find it?
So Q = nCvdT + pdV to find the heat expelled for process d to a.

Thanks for any clarification and help, I am really lost here.
 
Last edited by a moderator:
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Anyone?
 
Hi. Yes, you would use Q = ΔU + W to get the heat added or expelled for each path segment. Q is positive for heat added, and negative when heat is expelled.
 
How does the temperature at c compare to the temperature at b? Use that to determine the heat flow from b-c.

How is the net work done by the system related to the heat in and heat out?

AM
 

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