Physics 237 17.2 - First Law of Thermodynamics Two closed...

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1 First Law of Thermodynamics Two closed thermodynamic cycles for an ideal gas are depicted on the pV diagram. Imagine processing the gas clockwise through Cycle 1 once. Determine whether the change in internal energy of the gas in the entire cycle is positive, negative, or zero. Δ U 1clockwise = 0 internal energy only depends on initial and final states Imagine processing the gas clockwise through Cycle 1. Determine whether the work done on the gas in the entire cycle is positive, negative, or zero. Two closed thermodynamic cycles •W 1clockwise < 0 negative to the right, positive to the left, zero along the vertical sides (isochoric). W = - area of rectangle. Imagine processing the gas clockwise through Cycle 1. Determine whether the heat energy transferred to the gas in the entire cycle is positive, negative, or zero. Q 1clockwise > 0 positive because W is negative and Δ U = W + Q = 0 Demo:steam engine
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2 A cylinder with initial volume V contains a sample of gas at pressure p. The gas is heated in such a way that its pressure is directly proportional to its volume. After the gas reaches the volume 3V and pressure 3p, it is cooled isobarically to its original volume V. The gas is then cooled isochorically until it returns to the original volume and pressure. Find the work W done on the gas during the
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This note was uploaded on 09/09/2011 for the course PHYSICS 142 taught by Professor Hoffman during the Spring '09 term at Ill. Chicago.

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Physics 237 17.2 - First Law of Thermodynamics Two closed...

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