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Gas in space

  1. Dec 8, 2007 #1
    Bulb with volume of 5 liters is filled with nitrogen n = 3 molls. The bulb is set in space, the bulb cracks and the gas starts to expand. The nitrogen is considered as a real gas. Find the change in temperature. Joseph van der Waals' constant equals 0.137.
     
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  3. Dec 8, 2007 #2

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    In van der Waal's eqn of state, there are two constants. Or am I going in the wrong direction?
     
  4. Dec 8, 2007 #3
    Well that is how the problem is given.
     
  5. Dec 8, 2007 #4

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    Do you know the answer?
     
  6. Dec 8, 2007 #5
    Yes, its -6.6K.
     
  7. Dec 8, 2007 #6
    Anybody, somebody...
     
  8. Dec 8, 2007 #7

    Danger

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    All that I'm sure of is that if I cracked one in space after my traditional bacon & jalepeno breakfast sandwich, I could be half-way out of the solar system before I realized that I couldn't breathe.
     
  9. Dec 9, 2007 #8
    Come on guys, think....
     
  10. Dec 9, 2007 #9
    What was the temperature of the gas in the bulb before it cracked?

    So you have ab out 74 grams of Nitrogen (assuming N2 gas) in a 5 litre space at a pressure of (oddly enough) about Avagadro's number of atmospheres. (22.3)

    I got all that stuff.

    I can do the standard: nRT=(V-nb)((P+(n*n*a)/(v*v)) versus the standard P=nRT given that you have supplied the "a", thanks, but can you give the temperature.

    Juast as a SWAG I would guess and it is nothing more than that a difference on the order of about 0.45%

    But I can't give you the final answer without knowing the starting temperature and where the object is. Is it in direct solar sunlight in space? In the shade? Or am I misreading your intent?
     
  11. Dec 10, 2007 #10
    There is no information about the location of the bulb. Its mentioned that the bulb is made of some kind of highly melting metal.
     
  12. Dec 10, 2007 #11

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    What is the unit of the constant you have mentioned?

    In the table for van der Waals' constants, the values for nitrogen is not at all close for either a or b to 0.137.
     
  13. Dec 10, 2007 #12
    Well as I checked it couple of tables in my books and on the internet 0.137 is quite reasonable number.
     
  14. Dec 10, 2007 #13

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    For which one?
     
  15. Dec 10, 2007 #14
    In my problem a = 0.137 Nm^4/mol^2
     
  16. Dec 10, 2007 #15
    In my problem a = 0.137 Nm^4/moll^2

    Considering that van-der Waals` formula is (P+a/V^2)(V-b)=RT for one moll of matter.
     
  17. Dec 10, 2007 #16

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    Hi duvix,

    Do you know the thermodynamic state of the nitrogen given this information? Why not? What additional information would you need? (hint: you don't know the state from this info)

    Do you know anything about the final state of the gas from this? What do you need to determine final state?

    If you don't know the initial state, don't know the final state, what can this mean? What are they asking for? Are there any simplifying assumptions you need to make and if so, what are they? (hint: regardless of initial and final states, is there a relationship between them?)
     
  18. Dec 10, 2007 #17
    Actually the state is given as gaseous. After the bulb cracks, it expends as gas.
     
  19. Dec 10, 2007 #18

    Q_Goest

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    By state, I don't mean solid, liquid or gas. Knowing something is a liquid or gas does not give us enough information to determine the pressure, temperature, internal energy, entropy, density, etc... We need to know two of these things to know its thermodynamic state. Pressure and temperature are the most common two. The question as posed doesn't provide sufficient information to determine its thermodynamic state.

    The OP provides only enough information to determine density. We can assume there is some pressure and temperature, but those variables can be almost anything since there is no way to pin down any second piece of information about the state. Remember, you need 2 pieces of information to determine the state such as density and temperature. From that, you can calculate the pressure.

    Similarly, you can't determine the final state. Nor can you determine any of the states the nitrogen may transit as the gas expands and leaves through the crack in the container.

    So what is the OP really asking? You can't assign any values to any of it. The best you can do is write the equations which describe how the nitrogen transists the various states, and input the variables you do know. I don't think the OP is looking for a difinitive answer, it is asking only for you to demonstrate how to calculate the future state of a gas given some initial, but undefined conditions. The bit about the Joseph van der Waals' constant is a bit missleading, perhaps intentionally so since you are told the nitrogen behaves as an ideal gas, thus - no additional information would be needed to plug into the ideal gas equation.
     
  20. Dec 10, 2007 #19
    Okay there is just one more fact. The bulb, is formed by pumping air into melted metal, cooled and only then moved into space and then happens what happens. By the way the teacher says that the problem is solvable.
     
  21. Dec 11, 2007 #20

    Q_Goest

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    If you made an assumption about the pressure when the metal was molten (can you think of what that is?) then you can determine the state of the gas at that point. But if you then say, you cool it down, then you have to make an assumption about what temperature it is being cooled down to. Somewhere along the line, if you really want to put numbers to this, you will need to make some assumptions about the state.
     
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