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Thread: A Gas Question

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    necroeire's Avatar
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    A Gas Question

    Will a cylinder full of Oxygen weigh the same at 20DegC than at 70DegC?

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    FactionOne's Avatar
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    This is probably worth checking as my recollections are hazy; and I guess it depends on exactly what tolerances you need to be working to (as I'm sure there is a "small" effect); but AFAIK the volume of the gas may change (because the density changes with temperature), but it's mass shouldn't (apart from that hair-splitting margin)...

    Regards,

    Rob.

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    And i thought this was about central heating again.

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    Is this one of those Aeroplane vs Conveyor belt threads?


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    tonedef's Avatar
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    Quote Originally Posted by necroeire
    Will a cylinder full of Oxygen weigh the same at 20DegC than at 70DegC?
    Of course it will, it'll just be harder to carry?
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    TDI-line's Avatar
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    And a little hotter.

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    Do you mean a cylinder of compressed oxygen as in a cylinder for an oxyacetelyne torch. If so then the weight will be the same as the mass of the gas has not changed its just that the internal pressure on the cylinder wall will be higher as the the gas at 70C has more energy and as such is at a higher pressure
    This is explained by the compined gas law shown below.

    P1 V1 / T1 = P2 V2 / T2

    P= pressure , V =volume and T =temperature in kelvin
    In this case the volume is constant as the cylinder does not change.
    Solving this we get the Pressure at 70C (343Kelvin) = 1.17 x pressure at 20C(293)
    Enda1

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    necroeire's Avatar
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    That's what I thought but, I was told by an expert from the gas company I'm building a system for....if the cylinder has 20% liguid O2 and 80% compressed O2 and the temperature increases - reducing the pressure by producing more gas, then there will be less liquid oxygen and more gaseous oxygen thus having a lower weight. The total mass will remain the same but the weight will decrease. I still don't understand this explaination but I'm sure he is right.

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    dummi's Avatar
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    weight is a function of mass , only thing that will change weight would be a change in gravity.
    just a little a6

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    Numptie of the highest order

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    I think I could see his logic if the gas / liquid was changing state, but I don't see how it can between those temps as it's boiling point is -180 degrees and even then I don't think it matters. I think it's mass and therefore weight would be constant all other things staying the same except temp.

  12. #11
    Yeee-haw
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    No change, it's a closed system. Nothing gets in, nothing gets out. Phase changes don't alter mass.

    Mike
    Last edited by Geordie Mike; 2nd October 2006 at 18:15. Reason: Missing one small but crucial word

 

 

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