Question about thermodynamic quantities

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SUMMARY

This discussion centers on the thermodynamic relationships involving enthalpy (dH) and internal energy (dU) during constant pressure processes. It establishes that dH equals dqp, indicating that reversible work is necessary for dw to equal zero, as dv remains constant. The conversation also explores the implications of irreversible heat transfer on qv and the conditions under which dU equals dqv, particularly in the context of ideal versus non-ideal gases. The participants clarify that the nature of the gas and the reversibility of the process significantly influence these thermodynamic relations.

PREREQUISITES
  • Understanding of thermodynamic processes, specifically constant pressure and constant volume.
  • Familiarity with the concepts of enthalpy (H) and internal energy (U).
  • Knowledge of reversible and irreversible processes in thermodynamics.
  • Basic principles of ideal and non-ideal gases.
NEXT STEPS
  • Study the implications of Joule's free expansion on non-ideal gases.
  • Research the characteristics of reversible versus irreversible heat transfer.
  • Examine the mathematical derivations of dH and dU in various thermodynamic processes.
  • Explore the conditions under which thermodynamic processes can be considered reversible.
USEFUL FOR

This discussion is beneficial for students and professionals in thermodynamics, particularly those studying chemical engineering, mechanical engineering, or physical chemistry, who seek to deepen their understanding of energy transfer and thermodynamic processes.

kelvin490
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We know that for constant pressure thermodynamic processes, dH=dqp. My question is, does it implies that only reversible work is possible in this processes so that dw=0 because dv is zero? In addition, does qv necessarily be reversible heat transfer in this case? What if the heat transfer is irreversible?

Similar question for dU=dqv, does the process need to be reversible?

Another question is, do the above relations have anything to do with whether or not the system is an ideal gas? I have heard from a lecture that du≠dqv in Joule's free expansion for non-ideal gas. Consider reversibility and whether it's ideal gas there are four combinations of situations (ideal gas reversible,ideal gas irreversible, non-ideal gas reversible, non-ideal gas irreversible). I get confused with how these factors affect the thermodynamic relations.
 
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Is it true that reversible process can only occur in the form of infinitesimal expansion/compression?
 

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