大學(xué)物理熱學(xué)

1、Maxwell-Boltzmann DistributionPhase transition2006-11-06Maxwell-Boltzmann分布率 的碰撞數(shù)等于反過來的逆過程的碰撞數(shù)時才能發(fā)生.現(xiàn)在他考慮的是兩個粒子碰撞的速度，而不是一個粒子的不同速度分量，存在統(tǒng)計的獨立性.1866年，Maxwell承認(rèn)他1860年的推導(dǎo)“may appear precarious” .接著，他指出平衡態(tài)的達(dá)到，只有在初始態(tài)碰到末態(tài)這樣他又給出了另一個推導(dǎo).這就意味著即同時類似于前面的推導(dǎo)，他得到 這時能量守恒的條件應(yīng)該是1868年，Boltzmann將這種考慮推廣到存在外力的情況，其中即在勢函數(shù)V(x

2、)的情況.然后Boltzmann采用Maxwell的推導(dǎo)方式，得到其中這就是著名的Maxwell-Boltzmann分布率.Temperature Dependence of Chemical ReactionsPhase TransitionPV=NkBTP low, T highEvaporationIn a LiquidSaturated Vapor Pressure1)Evaporation2) CondensationBoilingBoiling: PSVP=PExternalHumidityPartial PressureHumidityFor: 30oC, PP of water

3、 in the air 21.0 torr, thenSupersaturationFor: 30oC, PP of water in the air 21.0 torr, if T falls to 20oC (SVP=17.5 torr), then RH would exceed 100%, What would happen ?Dew or Fog or Rain might appear !Dew point as a measure of RH.Van der Waals Equation of StateVan der Waals in 1873:1) Finite size o

4、f molecules 2) Attractive forces between moleculesWhat would happen ?14.1 Van der Waals equationThe Nobel Prize in Physics 1910for his work on the equation of state for gases and liquidsJohannes Diderik Van der Waals (1837-1923) (1873)Van der Waals: 126 000 itemsVirial expansionCritical pointVan der Waals isothermsDimensionless version:wheretilde1. non-physical part (p 0)2. There is no solid pha