{"term":{"metadata":{"id":"03778","doi":"10.1351\/goldbook.M03778","code":"M03778","status":"current","longtitle":"IUPAC Gold Book - mean free path, λ","title":"mean free path","index":"quantity","version":"2.3.3","lastupdated":"2014-02-24"},"definitions":{"definition":[{"id":"1","html":"The average distance a molecule travels between collisions. For a molecule, <\/span>, where is the number of molecules per unit volume and is their mean diameter. For O_{2<\/sub><\/span> at one atmosphere and , this distance is only <\/span>; at <\/span> atmospheres and it is . For an aerosol<\/a> particle, the mean free path, in the Stokes<\/a> region (see Stokes law<\/a>) is given by: <\/span> where is the mass of the particle, is the Boltzmann constant<\/a> (<\/span>), is the temperature ()<\/span> and is the mobility<\/a>.","text":"The average distance a molecule travels between collisions. For a molecule, [math: λ = ( 2 π n d m 2 )-1], where [math: n] is the number of molecules per unit volume and [math: dm] is their mean diameter. For O2 at one atmosphere and [math: 25°C], this distance is only [math: 9.7 x 10E-6 cm]; at [math: 10E-6] atmospheres and [math: 25°C] it is [math: 9.7 cm]. For an aerosol particle, the mean free path, [math: λ B] in the Stokes region (see Stokes law) is given by: [math: λ B = 3 k T m m B] where [math: m] is the mass of the particle, [math: k] is the Boltzmann constant ([math: 1.381 x 10E-23 J K-1]), [math: T] is the temperature ([math: K]) and [math: B] is the mobility.","contexts":{"in":[],"of":[]},"chemicals":[],"links":[{"type":"goldify","url":"http:\/\/dev.goldbook.iupac.org\/terms\/view\/A00176"},{"type":"goldify","url":"http:\/\/dev.goldbook.iupac.org\/terms\/view\/S06027"},{"type":"goldify","url":"http:\/\/dev.goldbook.iupac.org\/terms\/view\/B00695"},{"type":"goldify","url":"http:\/\/dev.goldbook.iupac.org\/terms\/view\/M03955"},{"type":"internal","url":"http:\/\/dev.goldbook.iupac.org\/terms\/view\/S06028"}],"math":[{"meaning":null,"type":null,"latex":"\\lambda = (\\sqrt{2}\\ \\pi \\ n\\ d_{\\text{m}}^{2})^{-1}"},{"meaning":null,"type":null,"latex":"n"},{"meaning":null,"type":null,"latex":"d_{\\text{m}}"},{"meaning":null,"type":null,"latex":"25\\ ^{\\,\\unicode{x26ac}}\\text{C}"},{"meaning":null,"type":null,"latex":"9.7\\times 10^{-6}\\ \\text{cm}"},{"meaning":null,"type":null,"latex":"10^{-6}"},{"meaning":null,"type":null,"latex":"25\\ ^{\\,\\unicode{x26ac}}\\text{C}"},{"meaning":null,"type":null,"latex":"9.7\\ \\text{cm}"},{"meaning":null,"type":null,"latex":"\\lambda _{\\text{B}}"},{"meaning":null,"type":null,"latex":"\\lambda _{\\text{B}} = \\sqrt{\\frac{3\\ k\\ T}{m}}\\ m\\ B"},{"meaning":null,"type":null,"latex":"m"},{"meaning":null,"type":null,"latex":"k"},{"meaning":null,"type":null,"latex":"1.381\\times 10^{-23}\\ \\text{J K}^{-1}"},{"meaning":null,"type":null,"latex":"T"},{"meaning":null,"type":null,"latex":"\\text{K}"},{"meaning":null,"type":null,"latex":"B"}],"sources":["Green Book, 2nd ed., p. 56 [Terms<\/a>] [Book<\/a>]","PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)<\/em>) on page 2201 [Terms<\/a>] [Paper<\/a>]"]}]},"access":{"html":"http:\/\/dev.goldbook.iupac.org\/terms\/view\/M03778\/html","json":"http:\/\/dev.goldbook.iupac.org\/terms\/view\/M03778\/json","xml":"http:\/\/dev.goldbook.iupac.org\/terms\/view\/M03778\/xml","plain":"http:\/\/dev.goldbook.iupac.org\/terms\/view\/M03778\/plain","pdf":"http:\/\/dev.goldbook.iupac.org\/terms\/view\/M03778\/pdf","originalpdf":"http:\/\/iupac.org\/goldbook\/M03778.pdf"},"timestamp":"2019-01-19T02:32:27-06:00"}}}