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2more gchem

Discussion in 'DAT Discussions' started by tRNA, Apr 10, 2007.

  1. tRNA

    tRNA Member 10+ Year Member

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    Apr 28, 2005
    tried to think about these from all different angles but still can't understand the reason why each of the following happens:

    1) at moderately high pressure, a gas's volume is less than predicted. why?
    no clue!!

    2) at extremely high pressures, a gas's volume is more than predicted. why?

    is this reffering to the volume of the cotainer or the volume of the individual gas particles???
    i think it's the case where you violate the kinetic molecular theory, where under hi pressure the volume of the individual gas particles become more significant (therefore higher volume than predicted) since the distance between each of the particles is less significant than it used to be under low pressure, am i correct??
     
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  3. sickeye29

    sickeye29 New Member 2+ Year Member

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    Jul 20, 2006
    Los Angeles
    this is true of non-ideal gases or REAL gases because as pressure is exerted on molecules of the gases they are pushed closer together. but at extremely high pressures the molecules become so close that there intermolecular forces or electrons clouds cause them to repel each other thus making there volume larger than they appear.
    i believe this is right anyone correct me if im wrong.
     
  4. tRNA

    tRNA Member 10+ Year Member

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    Apr 28, 2005
    ok thanks sickeye, that make sense for the extremly hi pressure case, but if you think about this like a series, first the gas is ideal so it's at low pressure, so the volume of the gas particles is neglegible, then as we increase pressure moderatly the gas becomes more like a real gas so the volume should increase, or become more than predicted(ie more than the initial gas volume in the ideal state) but they're saying NO at this stage the volume will actually be less than predicted ( i am assuming that means less than the initial gas volume in the ideal state) and that's what i don't undersatand? why would the volume be less if we are increasing the pressure, it doesn't matter if we increase the pressure moderatley or extremly, the volume will increase as long as we are increasing the pressure right?!?
    then if you follow the series the next stage is the extremly hi pressure where the volume will be more than predicted and that make sense so plz explain that middle part, thanks again
     
  5. sickeye29

    sickeye29 New Member 2+ Year Member

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    Jul 20, 2006
    Los Angeles
    sorry im just confused now too
     
  6. llopop

    llopop 2+ Year Member

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    Apr 7, 2007
    Which text are you citing this question from? It seems as though the question wording should be reversed or their thinking is just plain incorrect.

    Q#1: Under moderate pressures a gas will exhibit MORE volume then expected due to the nature of gases and pressure. Gases behave as individual particles and occupy much more volume/h then the other states.

    However...

    Q#2: Under "extremely high pressures" gases exhibit LESS volume then expected. An ideal gas dosn't exist so you cannot considered it for this question. Try to find a Pressure/Volume graph for a real gas and these questions become clear. A real gas at extremely high pressures will state change to liquid, which exhibits much less volume then expected for a gas.
     

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