eli5: why does potassium react so violently with water but is harmless to us in let’s say a banana ?
In: 7
Potassium in a banana isn’t potassium *metal*, it’s the already-oxidized K+ ion floating around in banana juice.
Potassium metal hasn’t been oxidized yet, and reacts explosively with any electron acceptor (like water) to do so.
In bananas potassium is present as a salt. If for some reason potassium is not present as a salt, it will be trying to reach that form as fast as possible. And potassium is very good at that. Potassium, that is the potassium ion, ( disregarding the other exotic forms ) has a single positive charge ( sorry, this is no longer a proper eli5) which is the most common form it takes, which you have in bananas, soil, water and basically everywhere.
The other form, which is by no means common, but can be seen in laboratories is the element form. This is the one that reacts with water in a spectacularly quick fashion.
By it’s very nature potassium does not want to be in it’s element form and will do anything and everything to change the single charge ion form.
Sorry if there are typos, posted with my phone.
Edit: elemental form of potassium would be a lump of metal. It took scientists waaay to long to create potassium as that. It is so violently reactive. That is why whenever potassium is mentioned the form in which it is present never clarified. Basically it only appears as a harmless salt.
“Reacting violently” is something that a *molecule* does, not an *element*. Chemical reactions happen between molecules; and a different bunch of molecules containing the same element won’t usually behave the same.
Potassium metal reacts violently with water. But potassium chloride doesn’t. Potassium chloride is the *product* of reacting potassium metal with something containing chlorine. That reaction itself may be violent, but the resulting potassium chloride is a lot more passive.
(In fact, the word “passivating” is sometimes used for treating a metal to make it less reactive — usually something like steel, to make it less affected by corrosion.)
It’s a matter of potential energy.
Pure potassium has a lot of potential energy. When you oxidize it (for example by dropping it in water) that potential energy gets converted to light and heat. But now it’s already combined. That’s the state it’s in in a banana so you can’t get additional energy out of it.
Imagine a bowling ball on a pendulum that has been pulled back. That has a lot of potential energy. If you let go that energy is released, and if your face is in the way it will hurt. But once the ball stops swinging it’s already released the energy (possibly because it was transferred into someone’s face). You can give that bowling ball a big smooch and, aside from all your friends thinking you’re a weirdo, no harm would come.
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