nobodysuspectsthebutterfly asked:
sodiumlamp answered:
The short ‘n’ general answer is that hydrogen peroxide releases heat as it decomposes, because its decomposition products (oxygen and water) are more stable than hydrogen peroxide itself. If you can make a lot of hydrogen peroxide decompose all at once, it’s going to get hot enough to get noticed.
Like all peroxides, hydrogen peroxide has an oxygen-oxygen bond:
H-O-O-H
This O-O bond is rather weak, to the point where it can actually split apart with only a modest amount of heat, resulting in a pair of hydroxyl radicals.
H-O-O-H → HO• + • OH
This is what’s known as homolytic cleavage, where two bonded atoms split apart, and each atom takes one of the two electrons used in the bond. These hydroxyl radicals are very reactive, and this is what’s behind hydrogen peroxide’s potency as an oxidizer. It can destroy dyes in fabrics just like household bleach, or even cause flammable materials to ignite.
If the peroxide bond were more stable, it might be practical for the hydroxyl radicals to recombine into hydrogen peroxide, and the homolytic cleavage would be reversible. If this were so, hydrogen peroxide would be quite stable, and a bottle of it would simply exist in an equilibrium, with some of the molecules in the peroxide form, and others split apart into radicals.
H-O-O-H ⇋ HO• + • OH
But this isn’t how it works in the real world. The O-O bond is weak, which means that it takes some amount of energy to maintain it, and once the bond is broken, that energy is released as heat. While conditions may exist to reverse the cleavage, it takes far less energy to simply rearrange the hydroxyl radicals into molecules of oxygen and water, and this is what slowly happens inside any bottle of hydrogen peroxide solution. Given enough time, every single molecule of hydrogen peroxide in the bottle will break down.
2 H2O2 → 2H2O + O2
While heat is released through this process, it happens so gradually that it’s dispersed before it can raise the temperature of the surroundings. But if you speed up the decomposition, you can heat things up very quickly. An increase in pH or temperature will make hydrogen peroxide decompose faster, which is why it’s manufactured under slightly acidic conditions, and the dilute solutions are the safest, and it should be stored at room temperature.
But one other way to speed up the decomposition is to expose the stuff to a catalyst, and that’s where blood comes in.
I didn’t know blood had any significant reaction with hydrogen peroxide until today, so I went looking around for a video and found this one below. So heads up to anyone who’s squeamish, or any vampires out there who hate to see food go to waste.
As it turns out, blood contains an enzyme called catalase, which is specifically there to neutralize reactive oxygen species like hydrogen peroxide. While the reaction mechanism isn’t really well understood, the point is that catalase breaks down the hydrogen peroxide into water and oxygen. Of course, hydrogen peroxide would do this on its own eventually, but the catalase in blood makes this happen much, much faster. So all that energy is released at once, and that’s why the mixture of blood and hydrogen peroxide heats up the way it does.
But there’s nothing unique about the role played by the blood. Catalase can be found in other life forms, including plants and fungi, and there are other chemicals which will catalyze the decomposition of hydrogen peroxide. For example, potassium iodide is commonly used in the ‘elephant toothpaste’ experiment.
As you can see in the above gif, there’s steam coming off of the foam, because it’s hot from the reaction that just took place.
bee-squared-official
