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PeteSampras
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Has some sense write in the thermodynamics identity the terms TdS and dU at the same side of the equation and with the same sign? what would be this sense?For example PdV=TdS+dU
Why do you want them to be on opposite side or have different sign if they are on the same side? What is you reason?PeteSampras said:TdS and dU
It all depends on what you presuppose. Tds - Pdv = dU, presupposes Pdv is the Reversible work done by the system which should decrease its internal energy if heat is not allowed to enter the system. Naturally if Tds is defined as the reversible heat transfer to the system which tends to increase the internal energy of the system, then the equation clearly gives you the net change of internal energy between two infinitesimally close thermodynamic states.PeteSampras said:PdV= TdS-dU
PdV is always the work done by the system on the surroundings, which always tends to decrease internal energy, and TdS is always the heat transferred from the surroundings to the system, which always tends to increase internal energy. So there is only one correct way of writing the equation: $$dU=TdS-PdV$$This equation describes more than just reversible heat and work. It provides the interrelationship between the changes in U, S, and V between any two closely neighboring thermodynamic equilibrium states of a material.PeteSampras said:Then if I write PdV-TdS=dU
The assumption is that PdV is the work done by the system which tends to increase the internal energy, and TdS is the reversible heat from the system to exterior that tends to decreases the internal energy ?
yes if dV is positive. and also TdS will increase U if dS is positive.Chestermiller said:PdV is always the work done by the system on the surroundings, which always tends to decrease internal energy,
The thermodynamics identity, also known as the first law of thermodynamics, is a fundamental principle in thermodynamics that states that energy cannot be created or destroyed, but can only be transferred or converted from one form to another.
The thermodynamics identity is used in science to understand and analyze energy flow and transformations in various systems, such as in chemical reactions, heat engines, and biological processes.
The equation for the thermodynamics identity is: dU = dQ - dW, where dU represents the change in internal energy of a system, dQ represents the heat added to the system, and dW represents the work done by the system.
The thermodynamics identity is closely related to the concept of entropy, which is a measure of the disorder or randomness in a system. The second law of thermodynamics states that in any energy transfer or conversion, the total entropy of a closed system will always increase, which is reflected in the thermodynamics identity equation.
No, the thermodynamics identity is a fundamental law of nature and cannot be violated. It has been extensively tested and verified through various experiments and is considered one of the most well-established principles in science.