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Unformatted text preview: Page 1 of 10 Lecture 4 September 4, 2008 Barometric Distribution Law Supplemental Reading: Chapter1_Supplement_BarometricDistLaw.pdf Why is it difficult to breathe at higher elevations? Why does it take longer to cook at higher elevations? The Barometric Distribution Law: 1. Assume isothermal conditions 2. Consider a cylindrical column of air from sea level (z = 0) rising to infinite height. Last time we considered the case where gas density was constant. Page 2 of 10 In reality, density is not independent of height so we will consider the gas to behave ideally: dz RT Mgp dz g dp i i i = = or dz RT g M p dp i i i = = z i p p i i dz RT g M p dp i o , i or z i p p i | z RT g M | p ln i o , i = z RT g M p ln p ln i o , i i = or z RT g M p p ln i o , i i = z RT g M p p ln i o , i i = M i must be in units of kg/mol = z RT g M exp p p i o , i i or = z RT g M exp p p i o , i i equivalent expressions (mass densities, i , and molar concentrations n or i c ~ ) : = z RT g M exp i o , i i and = z RT g M exp c ~ c ~ i o , i i To use these expressions for a mixture, treat each gas independently. 1. Calculate the amount of each gas at each elevation (z) based on the composition at z = 0 (normally 1 atm total pressure)....
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