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# Quiz5 - ∆ U or are they the same Explain 2 We apply a...

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7A -C/D Win 09 Quiz 5 DL Sec Last 6 digits ID # Name (Last, First) Grade Consider a piston containing 1 mole of diatomic H 2 gas (molecular weight = 2 g/mol) and 5 moles of monatomic Ar (atomic weight = 40 g/mol), with both gases initially at T = 300 K. The temperature remains low enough in all problems so that the vibrational modes of the H 2 remain completely frozen. The gases are always in equilibrium with each other, so they both have the same temperatures. 1a) Which gas has higher average molecular speed, or are they the same? Explain. 1b) If we increase the temperature by 20 K, which gas has a larger change in internal energy (
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Unformatted text preview: ∆ U), or are they the same? Explain. 2) We apply a heat source to the piston and measure 70 J transferred to the gases as heat. At the same time the gases expand, doing 30 J of work on the piston. The gases are at the same (new) temperature at the end. What is the change in internal energy ( ∆ U) for the 5 moles of Ar? Explain. E Th + E Bond = U ∆ U = Q + W KE = (1/2)mv^2 E Bond = 0 for gases. E Th = (1/2)k B T * (total modes) = (1/2)nRT * (modes per molecule) k B = 1.38 x 10-23 J/K R = 8.31 J/(K*mol) Possible types of energy modes for gases: KE trans , KE rot , KE vib , PE vib...
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