If I put an air-tight container into the fridge, how do the contents still get cold?
In: Chemistry
If I’m not mistaken this is the same concept of why hot contents in vacuum sealed containers/thermoses will inevitably lose heat, and why ice in vacuum sealed containers eventually melts versus keeping indefinitely.
When an object is cold, that just means it has less heat energy. When you put a container in the fridge, the contents get cold because the heat energy that is inside the contents of the container will transfer to the container itself, and then from the container to the cold air in the fridge.
Heat always travels warm -> cold, and it doesn’t care whether there’s physical barriers in the way, because it travels *in* the physical objects
The same way the earth gets warm from the sun. Space is essentially a gargantuan vacuum (air tight in an odd sense). Heat will radiate through this medium, albeit slower than any other method
The warm air molecules inside the container strike the walls of the container itself, transferring some of their energy (and, thus, heat) to the container itself.
The cold air molecules outside the container strike the walls of the container and some of the energy (heat) from the container transfers to the air molecules outside of it.
Through this process, heat from inside the container makes its way outside the container, until all three are equalized.
Coldness is just heat being leeched out of something.
Heat doesn’t only transfer through air. It also transmits through materials, some better than others. Plastic isn’t great at transferring heat, but it’s not terrible either. So when you put a container in the fridge, the container is losing heat to the refrigerator, and in turn, the food loses heat to the container, until they reach equilibrium at the fridge’s set temperature.
The air inside the fridge cools the container, the container cools the air inside the container, the air inside the container cools the food.
All those interfaces slow down the process so your food will cool down much slower than if it was directly in the fridge on an open plate but the cold will get to it eventually.
Being air tight only reduces one form of heat transfer: convection. But it doesn’t even affect that much, since the container takes on the temperature of the food and then convection can occur between the container and the fridge.
Air-tight doesn’t mean air-free. Air-tight containers seal the existing air in and outside air out. But it’s not under a vacuum. All those molecules both in and out are still moving and transferring heat.
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