Why is entropy a state variable even for irreversible path?

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SUMMARY

Entropy (S) is classified as a state variable or state function due to its path-independent nature, as defined by the integral of dS = dQ/T. This path-independence holds true for reversible processes; however, it does not apply to irreversible processes. Despite this, textbooks assert that S remains a state variable regardless of the process type. To calculate the change in entropy for a system undergoing an irreversible process, one can refer to the methodology outlined in the provided resource.

PREREQUISITES
  • Understanding of thermodynamic principles, particularly the laws of thermodynamics.
  • Familiarity with the concept of state functions in thermodynamics.
  • Knowledge of reversible and irreversible processes.
  • Basic calculus, specifically integration techniques related to thermodynamic equations.
NEXT STEPS
  • Study the derivation of the entropy formula dS = dQ/T in detail.
  • Explore the implications of irreversible processes on thermodynamic systems.
  • Learn about the concept of thermodynamic equilibrium and its significance in entropy calculations.
  • Review the provided resource on calculating entropy changes in irreversible processes.
USEFUL FOR

This discussion is beneficial for students and professionals in thermodynamics, including physicists, engineers, and anyone seeking to deepen their understanding of entropy and its role in both reversible and irreversible processes.

goodphy
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Hello.

The entropy S is a state variable or state function as the integral of dS = dQ/T is a path-independent, provided that the path is reversible process path. However, such a path-independency of the integral breaks down when the path includes irreversible process. So, I guess we can only say that S is a state variable only if there is no irreversible process, but the textbook said S is the state variable no matter the process includes irreversible process or not.

Well..if there is at least one irreversible process path along which the path-independency doesn't hold, how can I justify that S is a state variable?

I would like to get your help to clarify this confusion.
 
Science news on Phys.org
Suppose you had an irreversible process path that took your system from thermodynamic equilibrium state A to thermodynamic equilibrium state B. How would you determine the change in entropy for your system?
 

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