Fundamental Thermodynamic Relation

In thermodynamics, the fundamental thermodynamic relation is generally expressed as an infinitesimal change in internal energy in terms of infinitesimal changes in entropy, and volume for a closed system in thermal equilibrium in the following way.

Here, U is internal energy, T is absolute temperature, S is entropy, P is pressure, and V is volume.

This is only one expression of the fundamental thermodynamic relation. It may be expressed in other ways, using different variables (e.g. using thermodynamic potentials). For example, the fundamental relation may be expressed in terms of the Helmholtz free energy (F) as:

Read more about Fundamental Thermodynamic Relation:  Derivation From The First and Second Laws of Thermodynamics, Derivation From Statistical Mechanical Principles

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