burge_ch11_notes

burge_ch11_notes - Chapter 11 Gases 2011 Donald L. Siegel,...

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©2011 Donald L. Siegel, All Rights Reserved Chapter 11 Chapter 11 Gases
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©2011 Donald L. Siegel, All Rights Reserved States of Matter States of Matter W Solid - definite shape W Liquid - fluid, adopts the shape of the container that holds it, incompressible W Gas - fluid, fills the entire container, compressible W Other rarer states Plasma - sea of ions and electrons, found in stars
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©2011 Donald L. Siegel, All Rights Reserved Molecular Model of Gases Molecular Model of Gases W A model in science is a simplification we use to describe complicated phenomena. W The model is to treat molecules as separate, unreactive spheres No interactions other than to bounce off each other or the walls Rapid motion ~300 m/s. Collisions transfer momentum Volume of particles negligible
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©2011 Donald L. Siegel, All Rights Reserved
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©2011 Donald L. Siegel, All Rights Reserved More on the Model More on the Model W While each molecule is traveling with a random speed and direction, there is an average speed (kinetic energy ½mv 2 ) The average speed is determined by the temperature Temperature and kinetic energy are 2 forms of the same thing.
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©2011 Donald L. Siegel, All Rights Reserved Kinetic Model Kinetic Model - - Review Review W Molecules behave independently W Volume of particles is insignificant W Particles travel in straight lines until collisions change direction W Particles have no effect on each other except to collide
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©2011 Donald L. Siegel, All Rights Reserved Distribution of Speeds Distribution of Speeds W Kinetic model says average kinetic energy determined by temperature W It doesn’t mean that every molecule has the same speed W It’s the average that’s fixed by the temperature Different kinds of averages (see later) <E k > = ½m<v> 2 = 3/2RT u=(3RT/M) 1/2
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©2011 Donald L. Siegel, All Rights Reserved Maxwell Distribution Maxwell Distribution
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©2011 Donald L. Siegel, All Rights Reserved Example Example W What is the average speed of a water molecule at 400K? ( ) 01802 . 0 400 314 . 8 3 3 = = M RT u rms u rms = 744 m/s
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©2011 Donald L. Siegel, All Rights Reserved s m mol kg mol s m kg mol kg K K mol J M RT / / / 3 1 2 2 1 1 = = = R should be 8.314 J mol -1 K -1 M should be in kg/mol Doesn’t matter for relative rates. For 2 gases at the same temperature and pressure: A B A B B A M M t t r r = =
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©2011 Donald L. Siegel, All Rights Reserved Diffusion and effusion Diffusion and effusion W When substances mix, the process is called diffusion tends to be a slow process W When one or more substances escape through a permeable barrier, it is called effusion He leaking out of a balloon is effusion W Both processes depend on temperature and molar mass Time inversely proportional Rate directly proportional A B A B B A M M t t r r = =
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©2011 Donald L. Siegel, All Rights Reserved
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©2011 Donald L. Siegel, All Rights
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This note was uploaded on 02/20/2012 for the course 160 161 taught by Professor Kim during the Fall '08 term at Rutgers.

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burge_ch11_notes - Chapter 11 Gases 2011 Donald L. Siegel,...

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