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Choice of pressure when using ideal gas equation

  1. Dec 23, 2012 #1
    100g of CO are contained in a weighted piston-cylinder device. Initially, the CO is at 1000kPa and 200°C. It is then heated until 500°C. Determine the final volume of the CO treating it as an ideal gas.

    This is what my lecturer gave in his solution:

    V2=(mRT2)/P=(0.1kg*0.2968kPa.m3/kg.K*(500+273)K)/1000kPA

    My question is: why is the original pressure (1000kPa) been used instead of the final pressure?

    Thanks for your help.
     
  2. jcsd
  3. Dec 23, 2012 #2

    DrDu

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    Science Advisor

    Because initial and final pressure are equal as long as the weight on the cylinder remains the same.
     
  4. Dec 23, 2012 #3
    You can also use Charles Law to calculate the final volume, having calculated the initial volume from the universal gas law.
     
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