Question about thermodynamics first law

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The discussion clarifies that the equation dU = TdS - PdV is not limited to reversible processes but is a fundamental relationship applicable to any thermodynamic state. It emphasizes that this equation reflects the physical properties of a material, linking changes in internal energy (U), entropy (S), and volume (V) between neighboring equilibrium states. The relationship is derived from the second law of thermodynamics, which establishes constraints on these state functions. Despite being developed from reversible processes, the equation's applicability extends beyond them. Overall, the key takeaway is that dU = TdS - PdV is a state function relationship, independent of the process type.
Clara Chung
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I know that dS=dQ/T for reversible process,
is dU=TdS-PdV for reversible process only?
 
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Clara Chung said:
I know that dS=dQ/T for reversible process,
is dU=TdS-PdV for reversible process only?
This equation has nothing to do with any process. It is a physical property relationship that must be satisfied for any material, describing the relationship between the mutual changes in U, S, and V between and two closely neighboring thermodynamic equilibrium states of the material. This constraint is imposed as a consequence of the 2nd law of thermodynamics.
 
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Agree with Chestermiller, dU = TdS-pdV is nothing to do with the process, (reversible or irreversible), even though it is developed from the reversible process, since all of the qualities here are state functions. Therefore, they are just related to the state.
 

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