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10_1425_web_Lec_34_GasProcessesHeatTransport

10_1425_web_Lec_34_GasProcessesHeatTransport - Gas...

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Gas Processes and Heat Transport Physics 1425 Lecture 34 Michael Fowler, UVa
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The First Law of Thermodynamics A closed system has a total internal energy E int . This energy can be changed in two different ways: A. The system can do work W , or have work done on it, - W. B. Heat Q can flow into the system, or - Q flow out. The First Law is just total energy conservation: Δ E int = Q W Change in internal energy = heat in – work done.
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States of an Ideal Gas Suppose we have n moles of an ideal gas in equilibrium in a piston. The “state” of the gas can be defined by giving the state variables P , V. The gas state is a point in the ( P , V ) plane . If heat is exchanged or work done, the gas state variables trace a path in the ( P , V ) plane. If the gas moves along an isotherm PV = constant , its internal energy stays the same. Z P V The temperature (and therefore internal energy) is constant along an isotherm, PV = const.
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