Question about thermodynamics first law

[Clara Chung]

I know that dS=dQ/T for reversible process,
is dU=TdS-PdV for reversible process only?

 

[Chestermiller]

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.

 

[RedCliff]

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.