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Exothermic reactions are essentially reactions that release energy as heat (in part, at least) to the surroundings, and may cause an explosion or combustion, depending on the amount of heat released and the specific conditions (see this story as an example of an unexpected exothermic reaction at home).

We mix up all kinds of stuff at home, mostly in the kitchen, and each "ingredient" may be composed of numerous distinct chemical compounds. This huge number of possible combinations might make it probable that a redox reaction, which may be exothermic and there's no telling how much exothermic, will happen from time to time when mixing two (or more) foodstuffs together. However, it is pretty rare to hear about significant exothermic reactions that may be called "a household accident", such as the one I brought earlier.

My question is: how is this so? Is there any energy threshold that we do not normally cross in the kitchen? Or are the concentrations not large enough? How come kitchen chemistry is not more violent than it actually is? What makes "experimental" food chemistry safe for billions of people without chemistry knowledge?

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    $\begingroup$ Cool question. My first though is that we've been cooking things since the stone age, and any recipe containing a violently exothermic, or otherwise deadly, product or intermediate, would not have made its way into modern non-kitchen-blowing-up cookbooks ;) $\endgroup$ – airhuff Feb 6 '17 at 6:32
  • $\begingroup$ @airhuff, that sounds quite right, as evolution and natural selection can usually explain surviving trends and behaviors throughout history. But I don't want you to get off that easily... your comment may be true for basic foodstuffs and cooking methods that have been known since the beginning of recorded history, but what about all those new food products that are constantly being developed, usually by physical and chemical processes meant for longer preservation, better taste, etc. These have not yet been subjected to evolution, but are still experimentally safe... Thanks for your comment! $\endgroup$ – Don_S Feb 6 '17 at 7:09
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    $\begingroup$ New products and methods can indeed be more violent. Try to boil an egg in a microwave, for instance. $\endgroup$ – Ivan Neretin Feb 6 '17 at 7:29
  • $\begingroup$ Point absolutely taken, both Don_S and @IvanNeretin. The world of cooking has changed as drastically as the rest of the world in the past century. $\endgroup$ – airhuff Feb 6 '17 at 8:14
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    $\begingroup$ I don't exactly get the point here. We're using combustion all the time as source of heat and yes it's dangerous... If you really want to get into food itself, its burnt all to often if you're not careful, or want to use flambe technique. $\endgroup$ – Mithoron Feb 6 '17 at 22:46
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Life on Earth happens in pretty tight chemical limits, except for some exotic organisms we rarely encounter.

So, on the human side, the stuff we want to eat is not really very reactive. Carbohydrates, fats and proteins will give you no great fireworks no matter how you mix the three of them. The trace elements we need would be capable of some spectacular reactions, but we don't eat them in their pure form.

Which brings me to the "what is available" side. for almost all of human history, humans ate what they found in nature. And the stuff that reacts violently when mixed with organic matter is not really lying around to be used as an ingredient. Sure, some natural events are capable of producing pure oxygen, fluorine, or whatever, but they don't lie around for a long time waiting to be harvested, they react away. And plants and animals (=our food) tend to evolve in a way such that their bodies use the nitrogen and sulfur to build amino acids, not TNT and sulfuric acid.

There are a few substances in the kitchen which can give you a bit of a bang when mixed. If you want to impress a second grader, such classics as baking soda + vinegar, or mentos + cola will do nicely. But stuff which tends to pack more energy, and likes to free it in a flash, is not really food. You will notice that you need advanced processing methods to get all these ingredients - even though some of them (vinegar fermentation) were known in antique times, they are not something that grows on trees.

You can certainly find some edge cases - I keep pure NaOH on hand for pretzels, it is also used for some styles of noodle - but they are rare and concern ingredients which are not willy-nilly mixed into random dishes.

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