Understand Irreversible & Reversible Processes - Intro to Thermo of Materials

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Discussion Overview

The discussion centers around the concepts of irreversible and reversible processes as presented in the context of thermodynamics, specifically within materials science. Participants seek clarification on these concepts and their implications in practical scenarios, including calculations related to work in thermodynamic processes.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion regarding the explanation of irreversible and reversible processes in a textbook, seeking further clarification.
  • Another participant suggests that the original poster should provide specific excerpts from the textbook for more targeted assistance.
  • A participant defines a reversible process as one that produces no entropy and allows for a return to the initial state, emphasizing the need for slow progression to maintain equilibrium.
  • There is a question raised about the relationship between work and the expression 2PV, indicating uncertainty about its validity in the context of reversible processes.
  • Another participant clarifies that work is represented by the area under the curve on a P-V diagram, suggesting a more nuanced understanding of work in thermodynamic processes.
  • A further elaboration on the work done in a reversible process at constant pressure is provided, explaining how to visualize this on a P-V diagram.
  • A later reply indicates that one participant has gained understanding from the discussion.

Areas of Agreement / Disagreement

The discussion reflects a mix of understanding and confusion regarding the concepts of reversible and irreversible processes. While some participants provide definitions and explanations, there is no consensus on the specific mathematical expressions related to work, indicating ongoing uncertainty.

Contextual Notes

Participants reference specific conditions under which work is calculated, such as constant pressure and the need for volume change, but these assumptions are not universally agreed upon. The discussion does not resolve the validity of the expression 2PV in all contexts.

asdf1
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I'm reading the book, "Introduction to the Thermodynamics of Materials" (4/e) by David R. Gaskell. There's a section on pg42 explaining irreversible and reversible process, but I have no clue what the point is... Can someone explain it, please?
 
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I really doubt your going to get an answer. You probably should copy down whatever is troublesome for you and post it here.
 
Reversible process = no entropy production. Or to put it another way, you can turn the process around and go back to the exact same condition that you started with. You can think of it as the process that will be the best (theoretically) you can hope for. A reversible process means that to go from state 1 to 2, the process has to happen very slowly so that equilibrium is reached at every small step.
 
does the work always equal 2PV? I think that's what the textbook is trying to say...
 
Work is the area under the curve on a P-V diagram.
 
asdf1 said:
does the work always equal 2PV? I think that's what the textbook is trying to say...

In order for work to be done, there must be a change in volume. Because of this, 2PV doesn't really mean anything. Take a reversible process at constant pressure. Imagine a piston-cylinder set up. The volume is slowly increased as to keep the process reversible and to keep pressure constant. Now, if you draw the process on a P-v diagram, it will be a straight (horizontal) line. The work can be calculated by integrating [or since its a rectangle, P(v2-v1)].
 
:) i understand now~
thanks!
 

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