Lecture09_10 - Physics19: GreatIdeasofPhysics Lecture9:...

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Click to edit Master subtitle style Physics 19: Great Ideas of Physics Lecture 9: The Atomic Theory and Statistical Mechanics
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Reminders The Midterm is a week from today Covers all material through this lecture Chapters 1-5 of Spielberg and Anderson Chapters 1-2 of Lightman Closed book, closed note Short answer format No bluebook/scantron required
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Last Time Newton’s Laws do not distinguish between past and future Any process they allow is also allowed to happen in reverse Heat flow is an irreversible process From higher to lower temperature, never the other way around The Second Law of Thermodynamics: Using heat energy to do work always entails some “wasted” energy Entropy In a closed system, entropy always increases or stays the same So far only a mathematical construct – what does it really  represent? The atomic model
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A One-Dimensional, One-Atom Gas http://eee.uci.edu/10f/47311/demos.htm#OneAtomGas
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Gas Pressure and Average Speed The pressure exerted by a  gas on its container is due to  collisions (transfer of  momentum) Since momentum is conserved,  the change in momentum of the  gas molecule must go into the  wall of the container P = 1/3 Æ v2 = 2/3 K / V
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Gas Temperature and Average  The temperature of a  gas is proportional to  the  average kinetic  energy per molecule 3/2 k T = <Ek>          = ½ m <v2> The temperature is  closely related to the 
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Amadeo Avogadro (1776-1856) Practiced law in Turin before  becoming interested in  chemistry and physics Studied the amount of  materials consumed in  chemical reactions Found that “equal volumes of  all gases under the same  conditions of temperature  contain the same number of 
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Avogadro’s Number Avogadro estimated the number of  molecules in a particular volume of gas, the  very important “Avogadro’s Number”: 6.023   1023 = 1 mole Has no unit – it’s a pure number like “a dozen” This is about the number of Hydrogen atoms  in 1 gram of Hydrogen gas
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The Ideal Gas Law After Avogadro, Boyle’s Law and Gay- Lussac’s Laws could be combined into what  is today called the Ideal Gas Law: P V = N R T, or P V = n k T P is the pressure of the gas V is the volume of the gase N is the number of “moles” of gas n is the number of molecules
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Atomic Masses Avogadro found that different types of gases  have different weights per molecule,  however. He could measure this by their different 
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Lecture09_10 - Physics19: GreatIdeasofPhysics Lecture9:...

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