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Lect05

# Lect05 - Physics 213 Sept 7 2006 Physics 213 Sept 7 2006...

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Physics II: Heat & Electromagnetism today: Kinetic theory wrap-up 1st Law of Thermodynamics C V & C P of an ideal gas Paths on the pV –diagram Physics 213 Sept. 7, 2006 5.1 Translational Kinetic Energy and T Last time: • pV=Nk B T (ideal gas law) • pV=Nmv 2 rms /3 (kinetic theory) Total translational kinetic energy: K trans = ! Nmv 2 rms Physics 213 Sept. 7, 2006 5.2 Heat capacity of our simple ideal gas – , so Molar heat capacity at constant volume is C V : dQ = nC V dT At constant volume, the heat just increases the internal energy ( dQ = dK ), so: C V = 3 2 R Physics 213 Sept. 7, 2006 5.3 K = 3 2 nRT dK = 3 2 nRdT gas C V (J/mol·K) C V /R He 12.47 1.500 Ar 12.47 1.500 H 2 20.42 2.456 N 2 20.76 2.497 O 2 20.85 2.507 CO 20.85 2.507 CO 2 28.46 3.423 SO 2 31.39 3.775 H 2 S 25.95 3.121 Experimental Data Equipartition of Energy Theorem Each quadratic energy term (d f = “degree of freedom”) • KE= ! mv i 2, or • PE= ! kx i 2 for a molecule receives an average thermal energy of ! k B T ( ! RT/mole) Monatomic molecules: Diatomic molecules: Physics 213 Sept. 7, 2006 5.4 C V = d f 2 R

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First law of thermodynamics: " U = Q # W U =
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