asdf1
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When proving the equation,
dU=TdS-PdV
why is dw= PdV not dw= PdV +vdP?
dU=TdS-PdV
why is dw= PdV not dw= PdV +vdP?
The discussion centers on the thermodynamic equation dU=TdS-PdV and clarifies why the differential work done, dw, is expressed as PdV rather than PdV + VdP. It is established that work is only performed when there is a change in volume; thus, if volume remains constant, the pressure does not contribute to work done. The term VdP is identified as part of the internal energy change rather than work, reinforcing the distinction between work and internal energy in thermodynamic processes.
PREREQUISITESStudents of thermodynamics, physicists, and engineers seeking a deeper understanding of energy transfer and work in thermodynamic systems.
Work (force x distance) is done only if the pressure (force/area) acts over some change in volume (area x distance moved). If there is no change in volume, the force does not act over any distance - ie. the pressure just builds up but does not move anything (ie. it just increases internal energy). So, VdP is part of the internal energy of the gas, not the work done by the gas.asdf1 said:When proving the equation,
dU=TdS-PdV
why is dw= PdV not dw= PdV +vdP?