Isolated system

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Isolated system


The boundaries of isolated systems are impermeable for all forms of energy and matter. Changes of isolated systems have exclusively internal origins, e.g., internal entropy production, diS/dt, internal formation of chemical species i which is produced in a reaction r, dini/dt = drni/dt. In isolated systems some internal terms are restricted to zero by various conservation laws which rule out the production or destruction of the respective quantity.

Reference: »System

Internal change of internal-energy

IUPAC defines the internal energy change, ΔU = q+w [1]. This is restricted to closed systems. To clarify that internal (subscript i) and external (subscript e) energy changes, diU and deU, respectively, refer to U as "internal energy", it may be helpful to write "internal-energy" for U [2].
The First Law of Thermodynamics states that in all systems the internal change of internal-energy is always zero, diU/dt = 0 [2].


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  1. Cohen ER, Cvitas T, Frey JG, Holmström B, Kuchitsu K, Marquardt R, Mills I, Pavese F, Quack M, Stohner J, Strauss HL, Takami M, Thor HL (2008) Quantities, Units and Symbols in Physical Chemistry. IUPAC Green Book 3rd Edition, 2nd Printing, IUPAC & RSC Publishing, Cambridge. - »Bioblast link«
  2. Gnaiger E (1993) Nonequilibrium thermodynamics of energy transformations. Pure Appl Chem 65:1983-2002. - »Bioblast link«

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