How Does Volume Affect Internal Energy in Thermodynamics?

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Homework Help Overview

The discussion revolves around the relationship between volume and internal energy in thermodynamics, particularly in the context of an isothermal process involving a phase change from superheated vapor to saturated liquid. Participants are exploring the implications of the first law of thermodynamics and the use of specific formulas for internal energy.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the assumption that internal energy is solely a function of temperature, especially during phase changes. There is discussion about the role of volume and how it is accounted for in steam tables.

Discussion Status

The conversation is active, with participants clarifying their understanding of internal energy in relation to temperature and phase changes. Some guidance has been offered regarding the use of steam tables, but there is no explicit consensus on the broader implications of volume on internal energy.

Contextual Notes

Participants are navigating the complexities of thermodynamic principles, particularly in relation to phase changes and the assumptions made in standard calculations. The original poster's confusion stems from differing interpretations of the first law of thermodynamics in the context of their specific problem.

Amaelle
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Good day all !
I have a confusion regarding the use of the formula dU=CdT for computing internal energy for liquid or solid
like for instance in this exercice
entropy1.png


We have an isothermal process so I thought that dU=0 so according to the first law of thermodynamics
dQ=-dW (we want to calulate the heat transfer)
but the solution was totally different, for them dU is different from 0 ! (they got the values of u1 and u2 from tables)

any hint would be highly appreciated thanks!
 

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Is there a change of phase?
 
thanks for your prompt reply
yes, i think we went from super heated zone to saturated liquide
 
Amaelle said:
thanks for your prompt reply
yes, i think we went from super heated zone to saturated liquide
Is internal energy always just a function of temperature? Does internal energy change at constant temperature during a phase change?
 
Thanks a lot I got your point now!
because we are changing phase the temperature remains constant but still heat has been removed from the internal energy
internal energy does depend only on temperature when we are in the same phase.
thanks again!
 
Chestermiller said:
Is internal energy always just a function of temperature? Does internal energy change at constant temperature during a phase chang
Isn't internal energy depends on volume also.??
 
Apashanka said:
Isn't internal energy depends on volume also.??
That is taken into account in the steam tables, which the OP is using.
 
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