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0305 Notes

# 0305 Notes - A monatomic ideal gas held in a cylinder at...

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3/5/10 Oregon State University PH 202, Lecture 26 1 A monatomic ideal gas held in a cylinder at 200,000 Pa rises in temp- erature from 300 K to 900K as it expands isobarically. Then it is cooled isochorically to 225 K. If its original volume was 2 m 3 , fi nd the change in the thermal energy of the gas. 1. 100 kJ 2. 150 kJ 3. –100 kJ 4. –150 kJ 5. None of the above . (Does the answer depend on the processes or just the end state?)

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3/5/10 Oregon State University PH 202, Lecture 26 2 A monatomic ideal gas held in a cylinder at 200,000 Pa rises in temp- erature from 300 K to 900K as it expands isobarically. Then it is cooled isochorically to 225 K. If its original volume was 2 m 3 , fi nd the heat fl ow into the gas. 1. 650 kJ 2. 750 kJ 3. –650 kJ 4. –750 kJ 5. None of the above . (Does the answer depend on the processes or just the end state?)
3/5/10 Oregon State University PH 202, Lecture 26 3 Now suppose the gas in the previous problem is compressed isothermally back to its original volume (2 m 3 ), then heated isochorically to its original pressure (200,000 Pa). Before you even fi ll 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 +

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