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to Kinetics and Thermodynamics PageQuiz 2
Friday September 22
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1. What is the change in internal energy, D U, for an isothermal expansion of an ideal gas at 25° C from 1.0 L to 2.0 L ?
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The internal energy of a sample of ideal gas only depends on the temperature. However, for a real gas described, perhaps, by the van der Waals equation, upon expansion there will a change in intermolecular interactions and the portion of space occupied by molecular volume and thus even for an isothermal process D U is not zero.
2. What is D U for an ideal polyatomic gas for a process if the temperature rises from 25° C to 35° C?
Recall our discussion of the internal energy of an ideal monatomic gas and an ideal polyatomic gas.
For a polyatomic:
Um = 3RT + Um(0)
therefore D U = 3R D T for one mole assuming we neglect the vibrational contribution to internal energy which is temperature dependent. See Atkins page 48 and 56-57.
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