Thermodynamics - reversibility and heat addition

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SUMMARY

The discussion centers on the relationship between reversibility and heat addition in thermodynamics, specifically addressing the Clausius inequality. It is established that during a reversible change, more heat must be added compared to an irreversible change due to the generation of entropy in irreversible processes. This additional heat compensates for the entropy that is not generated in reversible processes, ensuring that the change of state adheres to the principles of thermodynamics. The participants clarify that the extra heat is necessary to maintain the same final states while adhering to the laws governing entropy.

PREREQUISITES
  • Understanding of the Clausius inequality in thermodynamics
  • Familiarity with the concept of entropy as a state function
  • Knowledge of reversible and irreversible thermodynamic processes
  • Basic principles of heat transfer in thermodynamic systems
NEXT STEPS
  • Study the implications of the Second Law of Thermodynamics
  • Explore the concept of entropy generation in irreversible processes
  • Learn about the mathematical formulation of the Clausius inequality
  • Investigate practical applications of reversible and irreversible processes in engineering
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Students and professionals in thermodynamics, mechanical engineers, and anyone interested in the principles of heat transfer and entropy in physical systems.

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I understand entropy is a state function, insofar as we deny the existence of irreversible cycles. However, for a said change of state, the heat transferred as a result of a reversible change is greater than that for an irreversible change. This is simply a reiteration of the Clausius inequality, as because entropy is a state function, a change dS is greater for a dq/T if dq is irreversible. However, it seems to me that it does not logically make sense for more heat having to be added for a reversible change. What is it about reversibility that requires more heat to be added to change states? I understand that entropy works out if the former statement is true; however, I guess I just don't understand how logically more heat is needed to effect a reversible change of state rather than an irreversible one. Where does the extra heat go if the final states are the same?

- Thanks
 
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You pretty much have it backwards. During an irreversible change, there is entropy generated within the system so, to get between the same two ends states with a reversible process, you need to compensate for the entropy which is not generated within the system during the reversible process by transferring additional heat into the system.
 

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