L10_26Jan_posted

# L10_26Jan_posted - Physics 6B Heat Work and the Ideal Gas...

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1 Physics 6B Heat, Work and the Ideal Gas Law 2 Housekeeping If you gave me a DRC form, please confirm via e-mail what you’ll need for midterm. Homework 2 solutions posted Practice Exam (from Spring 2009) posted Review session for midterm: Sunday 2/6, 7-9pm, Classroom Unit 2 Supplemental Problems ! extra-credit to make up lost homework points. . ! find them at the bottom of the assignments list on MP 3 Thermodynamics: using heat to do work Doing work on an object requires a source of energy… ! the energy source can be heat 4 Heat " Pressure " Force " Work Work is force acting over a distance ! W = F d Heat doesn’t create a force directly ! just increases thermal motion of atoms and molecules But heat can be used to increase pressure Pressure acting over a distance does work

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5 Ideal Gas Law -- Molar and Particle forms “Particle” form: PV = N k T ! N is number of particles ! k = 1.38 ! 10 -23 J/K is Boltzmann’s constant ! P,V in SI units “Molar” form 1: PV = n R T ! n is number of moles ! R = 8.314 J/(K·mol) is the “universal gas constant” ! P,V in SI units “Molar” form 2: PV = n R T ! n is number of moles ! R = 0.08206 (L·atm)/(K·mol) is the “universal gas constant” ! P in atmospheres ! V in Liters 6 Temperature, particle speed, particle energy Simple ideal gas model gave us… This relationship between particle speed and temperatures holds for complicated molecules as well as monatomic gases. We will see (soon) that relationship between T and internal energy is ! 1/2 kT per “degree of freedom” ! 3 degrees of freedom are associated with translational motion 7 Degrees of freedom The more independen t ways a molecule can move ! the more degrees of freedom it has. Single atom (“monatomic”) particles (e.g., helium, neon, argon…) ! 3 degrees of freedom, corresponding to x, y, z motion Two atom (“diatomic”) particles (e.g. H 2 , N 2 , O 2 …) ! add 2 rotational degrees of freedom for a total of 5 8 More degrees of freedom More complicated particles (e.g., H 2 O, CO 2 , NH 3 …) have an additional rotational degree of freedom for a total of 6
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L10_26Jan_posted - Physics 6B Heat Work and the Ideal Gas...

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