Ideal systems in classical thermodynamics

Abstract

The term `ideal' is currently employed for thermodynamic systems of different natures (gases, elastic systems, magnetic systems, etc). However, different meanings are usually given to this term. Joule's law, which establishes that the internal energy of a system depends exclusively on temperature, is considered here as a general criterion for an ideal system in classical thermodynamics. The conditions that a system should satisfy to obey Joule's law and the implications of these conditions on the equation of state are discussed. Some similarities and differences between ideal systems of different natures are also emphasized. Resumen. El término `ideal' se emplea en la actualidad para sistemas termodinámicos de naturaleza distinta (gases, sistemas elásticos, sistemas magnéticos, etc). Sin embargo, es habitual dar a este término distintos significados. La ley de Joule, que establece que la energía interna de un sistema depende sólo de la temperatura, se considera aquí como un criterio general para la condición de sistema ideal. Se discuten las condiciones que un sistema debe satisfacer para verificar la ley de Joule, así como las implicaciones de estas condiciones sobre la ecuación de estado. Se subrayan también las similitudes y diferencias entre sistemas ideales de distinta naturaleza.

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