My friend and I had a debate over this. He claimed a bag of dry ice would stay frozen longer if left out at room temperature because it would “create its own environment”. He said putting it in the freezer was like putting it in the oven because a freezer’s temperature is above the melting point of dry ice…and the freezer will work harder to keep the temperature constant??
So was my friend right??? Will Dry Ice melt faster in a Freezer than in your living room?
You could do a simple experiment. Get three equal masses of dry ice, put one in the freezer, one in a cooler, and one on the kitchen counter. The one on the counter will certainly sublimate first (that is, skip the liquid phase and go straight to gas) because of the large temperature differential, but I don’t know which of the cooler or freezer chunks would go first. It probably depends on how good the insulation on the cooler is, and its size. A small cooler would have less initial heat energy for the dry ice to absorb, and less surface area for heat from the outside air to transfer into the cooler.
The experiment is a good idea. One flaw in the reasoning is that Dry Ice will not melt at room temperature. Like sturmhauke said, dry ice will simply sublimate from solid to gas at room temperature. It actually sublimates at -109 F, so it’s not going to make much of a difference in the freezer. I would say that it would likely sublimate faster in warmer air, since more heat is getting to the substance, causing it to rise in temperature faster than if it was in a colder area, thus the sublimation should be faster.
Take water: If you put a pot of water on a 4000 degree piece of iron, it will boil very rapidly, and quickly evaporate into steam. If you put it on a fire at 213 degrees, it will slowly, slowly raise to the boiling point, and slowly turn to steam. I don’t know of a specific property that dry ice would have that would cause this trend to reverse. But I’m not a chemist, so what do I know.
I would expect that the sublimation (directly from solid to vapor) of dry ice in a small, enclosed space like a freezer would quite rapidly result in the atmosphere becoming a saturated with CO[sub]2[/sub] vapor. At this point further net vaporization of the dry ice would cease. Meanwhile in the room, which has a much larger volume of atmosphere to saturate, the dry ice would continue to sublime.
That is one possible flaw in the argument. I don’t think freezers are built to pump heat into the freezer. I think if it is too cold, they just shut off and don’t try to cool it any further. Some freezers may work that way, but your average household freezer? That would add expense, no?
The freezer should just shut off, it has no mechanism to increase temperature within it’s space. What you would have is the equivalent to a cooler, but a cooler full of frozen stuff, most likely.
That frozen stuff is still much warmer than the dry ice, and will transfer its heat causing additional sublimation. I do not know if there is any insulation between the freezer and refrigerator compartments, that will be another important factor. The refrigerator section could dump a fair amount of heat into the freezer section if there isn’t any insulation.
My guess is that the best bet would be a small, well insulated, empty cooler. That will give you the smallest amount of heat to be transferred to the dry ice, and keep it insulated against the ambient air. Leaving it out naked would cause all manner of convection currents to flow, and bring about the most rapid sublimation of all.
The higher temperature gradient outside of the freezer will cause a higher rate of heat transfer, therefore a higher sublimation rate. If you want to try it experimentally, do these things to make sure you are eliminating other variables:
While the compressor is running, a fan blows air over the coils and into the freezer. This will increase the heat transfer rate to the block of dry ice. Put up a protective barrier that will protect the ice from the wind yet will allow the air around the ice to be be at the same or similar temp to the air in the freezer. Create the same barrier for the one in the room (in case the barrier is insulating the ice - now each will have similar insulation).
Place each one on a similar surface, idealy have each on a styrofoam base, so that the heat losses from the surfaces are similar (if one is on a steel surface, it will melt faster than the other).
Make sure each block is the same shape and weight.
Putting the block in the freezer WILL NOT STOP SUBLIMATION due to partial pressure of CO2. At ambient temperatures above -101F (of whatever the sublimation temp is), the vapor pressure of CO2 is much higher than will be contained in the freezer. It probably only would take a couple inches of pressure to push the door open enough to vent the CO2.
If you don’t believe that, put some dry ice in an empty 2-liter bottle, cap it, place the bottle where the schrapnel from the exploding bottle will not damage anything or anyone, wait about 4 hours, then listen to the cannon-like explosion. That will prove to you that even partial pressures above 100psi will not keep dry ice from sublimating (although at those pressures, it does liquefy, so it is actually boiling, not sublimating).
Wooooooo doggies! You are soooooo correct! I’ve witnessed a 2-liter CO[sub]2[/sub] “bomb” go off, and it is LOUD! The concussion hits your tummy like a punch, and the bottle basically is reduced to a sheet - unless the cap gives first, in which case it flies off hard enough to dent a car door pretty badly. :eek:
I stand corrected. Live and learn.
Will ambient humidity contribute?
With high humidity, a layer of water ice forms on the surface of dry ice. If this has any appreciable effect on the rate of sublimation, then this would introduce a considerable variable between the freezer (low humidity) and room temp (high humidity) sample.
That could be an important variable, choosybeggar. If a thick layer of ice forms on it, it will definitely slow the heat xfer rate.
And the more I think of it, even though the freezer is obviously colder than the room, relative to the dry ice it is hot air. If the fan is circulating and the dry ice isn’t covered, the “wind” of the freezer might actually sublimate the dry ice more quickly than a block on the counter, especially one with a coat of (real) ice.
I think it’s time to experiment!
The (water based) ice will slow down the sublimation. If you try dry ice in a 2-liter bottle with water in it, the pressure shoots up very quickly, but then slows down as the dry ice gets a layer of ice on it.
End result is the same - a surprisingly percussive explosion.
Anthracite- I’ve seen a few CO2 2-liters go off. The first one I saw actually broke into lots of pieces, none bigger than 1 square inch. It was very cold outside that night, and that may have had something to do with it. The others seem to rip in half, usually through the thick part at the top, all the way down the sides, with the pieces held together with the bottom.
A college friend had one go off in his hand. It had baking soda and vinegar in it, so I don’t think it had quite the wollop (because the vinegar displaced what would have been high pressure CO2). His hand was quite swolen. And it went off indoors. I’ve never heard anything as loud as a 2-liter bottle expoding in a non-carpeted brick stairwell.