Editing Closed system (section)

===In thermodynamics===
{{main|Thermodynamic system}}
[[File:Diagram Systems.svg|thumb|Properties of isolated, closed, and open systems in exchanging energy and matter]]

In [[thermodynamics]], a closed system can exchange energy (as [[heat]] or [[mechanical work|work]]) but not [[matter]], with its surroundings.
An [[isolated system]] cannot exchange any heat, work, or matter with the surroundings, while an [[Thermodynamic system#Open system|open system]] can exchange energy and matter.<ref>[[Ilya Prigogine|Prigogine, I.]], Defay, R. (1950/1954). ''Chemical Thermodynamics'', Longmans, Green & Co, London, p. 66.</ref><ref>[[László Tisza|Tisza, L.]] (1966). ''Generalized Thermodynamics'', M.I.T Press, Cambridge MA, pp. 112–113.</ref><ref>[[Edward A. Guggenheim|Guggenheim, E.A.]] (1949/1967). ''Thermodynamics. An Advanced Treatment for Chemists and Physicists'', (1st edition 1949) 5th edition 1967, North-Holland, Amsterdam, p. 14.</ref><ref>Münster, A. (1970). ''Classical Thermodynamics'', translated by E.S. Halberstadt, Wiley–Interscience, London, pp. 6–7.</ref><ref>Haase, R. (1971). Survey of Fundamental Laws, chapter 1 of ''Thermodynamics'', pages 1–97 of volume 1, ed. W. Jost, of ''Physical Chemistry. An Advanced Treatise'', ed. H. Eyring, D. Henderson, W. Jost, Academic Press, New York, lcn 73–117081, p. 3.</ref><ref>Tschoegl, N.W. (2000). ''Fundamentals of Equilibrium and Steady-State Thermodynamics'', Elsevier, Amsterdam, {{ISBN|0-444-50426-5}}, p. 5.</ref><ref>Silbey, R.J., [[Robert A. Alberty|Alberty, R.A.]], Bawendi, M.G. (1955/2005). ''Physical Chemistry'', fourth edition, Wiley, Hoboken NJ, p. 4.</ref> (This scheme of definition of terms is not uniformly used, though it is convenient for some purposes. In particular, some writers use 'closed system' where 'isolated system' is used here.<ref>[[Herbert Callen|Callen, H.B.]] (1960/1985). ''Thermodynamics and an Introduction to Thermostatistics'', (1st edition 1960) 2nd edition 1985, Wiley, New York, {{ISBN|0-471-86256-8}}, p. 17.</ref><ref>[[Dirk ter Haar|ter Haar, D.]], [[Harald Wergeland|Wergeland, H.]] (1966). ''Elements of Thermodynamics'', Addison-Wesley Publishing, Reading MA, p. 43.</ref>)

For a simple system, with only one type of particle (atom or molecule), a closed system amounts to a constant number of particles. However, for systems which are undergoing a [[chemical equilibrium|chemical reaction]], there may be all sorts of molecules being generated and destroyed by the reaction process. In this case, the fact that the system is closed is expressed by stating that the total number of each elemental atom is conserved, no matter what kind of molecule it may be a part of. Mathematically:

:<math>\sum_{j=1}^m a_{ij}N_j=b_i</math>

where <math>N_j</math> is the number of j-type molecules, <math>a_{ij}</math> is the number of atoms of element <math>i</math> in molecule <math>j</math> and <math>b_i</math> is the total number of atoms of element <math>i</math> in the system, which remains constant, since the system is closed. There will be one such equation for each different element in the system.

In thermodynamics, a closed system is important for solving complicated thermodynamic problems. It allows the elimination of some external factors that could alter the results of the experiment or problem thus simplifying it. A closed system can also be used in situations where [[thermodynamic equilibrium]] is required to simplify the situation.