Class27 - Recall the situation of the last two clicker...

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3/9/12 Oregon State University PH 202, Lecture 27 1 Recall the situation of the last two clicker questions from last time— which involved these two gas processes: (a) A monatomic ideal gas held in a cylinder at 200,000 Pa rises in temperature from 300 K to 900K as it expands isobarically. (b) Then the gas is cooled isochorically to 225 K. Now suppose the gas is taken through two additional processes (continuing from its state after process b , above): (c) It is compressed isothermally back to its original volume (2 m 3 ). (d) Then it is heated isochorically back to its original pressure (200,000 Pa).
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3/9/12 Oregon State University PH 202, Lecture 27 2 Before you even fill in numbers , you can decide whether the values of W , E th , and Q for each process are positive, negative, or zero, by noting the gas’s changes in temperature (for E th ) and volume (for W ), then deducing the sign of Q , via subtraction: Process E th W Q (= E th W ) 1. Isobaric Expansion: + + 2. Isochoric Cooling: 0 3. Isothermal Compression: 0 + 4. Isochoric Heating: + 0 + Net for entire cycle : 0 + (You know the net work is negative because the area under the isobaric expansion curve is greater than under the isothermal compression curve.)
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3/9/12 Oregon State University PH 202, Lecture 27 3 And here are the numbers (all values in Joules): Process E th W Q
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This note was uploaded on 03/10/2012 for the course PH 202 taught by Professor Staff during the Winter '08 term at Oregon State.

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Class27 - Recall the situation of the last two clicker...

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