Effusion

Effusion

In chemistry, effusion is the process where individual molecules flow through a hole without collisions between molecules. This occurs if the diameter of the hole is considerably smaller than the mean free path of the molecules [K.J. Laidler and J.H. Meiser, Physical Chemistry, Benjamin/Cummings 1982, p.18] . According to Graham's law, the rate at which gases effuse (i.e., how many molecules pass through the hole per second) is dependent on their molecular weight; gases with a lower molecular weight effuse more quickly than gases with a higher molecular weight. For two gases at the same temperature (and having the same specific heat), and thus having the same kinetic energy, the average molecular speed of each gas can be found using the equation E=(1/2) mv^2. (To be more accurate, one would use the equation (3/2)"k"B"T" = (1/2)"mv"rms2 where "k"B is the Boltzmann constant and "v"rms is the root mean square speed of the gas molecules. The average speed would then be about 0.921 "v"rms.) Thus, lighter molecules have a higher speed. This results in more molecules passing through the hole per unit time. This is why a balloon filled with low molecular weight hydrogen left alone for a reasonable amount of time deflates faster than a separate balloon full of higher molecular weight oxygen.

See also

* Graham's Law of Effusion
* Diffusion

References

External links

* [http://library.thinkquest.org/12596/graham.html Graham's law]


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  • effusion — [ efyzjɔ̃ ] n. f. • av. 1150; lat. effusio, de effundere « répandre » 1 ♦ Vx Action de répandre (un liquide). Mod. EFFUSION DE SANG : action de faire couler le sang (dans une action violente). L ordre a été rétabli sans effusion de sang. 2 ♦… …   Encyclopédie Universelle

  • Effusion — Ef*fu sion, n. [L. effusio: cf. F. effusion.] 1. The act of pouring out; as, effusion of water, of blood, of grace, of words, and the like. [1913 Webster] To save the effusion of my people s blood. Dryden. [1913 Webster] 2. That which is poured… …   The Collaborative International Dictionary of English

  • effusion — Effusion. s. f. Espanchement. L effusion du vin dans les sacrifices. il y eut une grande effusion de sang. il se fait dans la joye une grande effusion d esprits. On dit au figuré, Effusion de coeur, pour dire, Cordialité, Grande demonstration d… …   Dictionnaire de l'Académie française

  • effusion — EFFUSION. subs. f. Épanchement. L effusion du vin dans les Sacrifices. Il y eut une grande effusion de sang dans ce combat. [b]f♛/b] On dit aussi au figuré, Effusion de coeur, pour dire, Vive et sincère démonstration de confiance et d amitié …   Dictionnaire de l'Académie Française 1798

  • effusion — c.1400, a pouring out, from M.Fr. effusion (14c.) and directly from L. effusionem (nom. effusio) a pouring forth, noun of action from pp. stem of effundere pour forth, spread abroad, from ex out (see EX (Cf. ex )) + fundere pour (see FOUND …   Etymology dictionary

  • effusion — d eaue, Effusio aquae. Il y eut plus grande effusion de sang au combat, Plus sanguinis in ipsa dimicatione factum …   Thresor de la langue françoyse

  • Effusion — (lat.), Ausströmung, Erguß; besonders das Ausfließen von Gasen aus einem sie rings umschließenden Gefäß, in dessen Wand eine Öffnung angebracht ist. Hierbei ist das Quadrat der Ausströmungsgeschwindigkeit dem Druck direkt und dem spezifischen… …   Meyers Großes Konversations-Lexikon

  • Effusion — nennt man die Diffusion von im Dissoziationszustand befindlichen Gasen durch poröse Diaphragmen, wobei im allgemeinen eine teilweise Trennung der Dissoziationsprodukte erfolgt, da deren Ditfusion unabhängig voneinander vor sich geht. Auf der… …   Lexikon der gesamten Technik

  • effusion — index expulsion, harangue, issuance, outflow, prolixity Burton s Legal Thesaurus. William C. Burton. 2006 …   Law dictionary

  • effusion — [n] outpouring address, diffusion, discharge, effluence, effluvium, efflux, emanation, emission, exudate, gush, gushing, ooze, outflow, pouring, shedding, stream, verbosity, wordiness; concepts 179,266 …   New thesaurus

  • effusion — ► NOUN 1) an instance of giving off a liquid, light, or smell. 2) Medicine an escape of fluid into a body cavity. 3) an instance of unrestrained speech or writing. DERIVATIVES effuse verb. ORIGIN Latin, from effundere pour out …   English terms dictionary

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