Why does a sealed baggie of dry ice lose weight over time at room temp, even before it pops and the gas escapes? I thought it might be due to buoyancy, perhaps? As the bag expands, it displaces air. But if that is the case, the why would it matter since CO2 is actually MORE dense than air, right? Please help me understand.

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    $\begingroup$ Simply because the bag is not 100% air-tight. CO2 keeps escaping. $\endgroup$
    – AChem
    Nov 6 at 1:12
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    $\begingroup$ Aside of gas diffusion through the walls, bag expansion by 1 L causes measured mass on scales is decreased by approx. 1.2 g. as that is equivalent to the buoyancy change. $\endgroup$
    – Poutnik
    Nov 6 at 6:06
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    $\begingroup$ The density relative to air is (mostly) irrelevant. As the volume expands, the buoyancy increases relative to the volume/mass of displaced air. Ships float because of the displaced mass of water (this is purely dependent on the mass they carry, not the density of the substance making up the mass). $\endgroup$
    – matt_black
    Nov 6 at 11:34


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