We can go from zero degrees Celsius to one hundred thousand in one second, like atomic bomb, but why does it take 24 hours to freeze about 5 kilograms of steaks to minus 25 degrees?

Answer

Dear Guido,

this question has just been answered. Then the question was:

Why is it possible to go from zero to tens of thousands of degrees of heat in less than one second, but does it take a lot of time to cool something down from, say, plus 20 degrees to minus 30 degrees?

And the answer is:

/ there is such a thing as nature’s pursuit of more disorder (≈ entropy). When something gets warmer, the particles in it move more relative to each other and you get more entropy. Also with an explosion you will start a chemical reaction that is exothermic (= where heat is released) and this will increase the entropy. There are a lot of possibilities to increase the entropy, to heat something up or to make the particles move more relative to each other (whatever you want to call it).

To cool something, on the other hand, is much more difficult. To get that done, you actually have to start heating up something else (total entropy still needs to go up). A cauldron of soup that cools down actually heats up the environment. When you’re making ice cubes, your freezer’s condenser (the tubular grid usually located at the back) will release heat into the environment. The heat exchange that happens in this way is much less efficient (try heating up a bowl of soup…) and will therefore be much slower.

So it actually comes down to the fact that the total entropy must always increase. This can be done in various ways. One is by extracting heat from an object (which will locally lower its entropy), but this is far from the most efficient way. The efficient ways (burning gas, sending electricity through a resistor, generating microwaves, an exothermic chemical reaction, …) we use to heat something up, but the less efficient (extracting heat from another object) is the only possibility that we have to cool something down…