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> This explains why fire is hot regardless of fuel composition. This cracks me up. Despite a chemistry degree, I have never really thought to consider whether
by kortex 6y ago
> This explains why fire is hot regardless of fuel composition.
This cracks me up. Despite a chemistry degree, I have never really thought to consider whether or not endothermic combustion exists, even though endothermic reactions exist. Nitrogen "combustion" with oxygen is endothermic. But really, the definition of combustion implies a high temperature, relatively rapid and self-sustaining reaction, e.g. rust and glucose metabolism aren't combustion.
- avmich 6y agoThere were reports of using small iron pellets as a fuel, so does it mean rust creation can be considered combustion as well?
- marcosdumay 6y agoIs it hot, relatively fast, and self sustaining? If you make your pellets small enough, it is. The combustion of steel brushes is quite interesting to watch. If you make your pellets too small, then is stops being an ordinary combustion and becomes an explosion.
- avereveard 6y ago"Iron burning in atmosphere of pure oxygen" https://www.youtube.com/watch?v=A7j14otCdyY https://www.youtube.com/watch?v=A7j14otCdyY
- scsilver 6y agoIf you get small enough, you start getting into the territory of dust explosions. https://en.m.wikipedia.org/wiki/Dust_explosion https://en.m.wikipedia.org/wiki/Dust_explosion Another interesting phenomenon is spontaneous combustion where exothermic reactions get hot enough to start the combustion process in a medium. https://en.m.wikipedia.org/wiki/Spontaneous_combustion#:~:text=Spontaneous%20combustion%20or%20spontaneous%20ignition,temperatures)%20and%20finally%2C%20autoignition https://en.m.wikipedia.org/wiki/Spontaneous_combustion#:~:te.... I was a fire engineer in a past life, forgot the science but remember the cool phenomenons.
- RRWagner 6y agohttps://www.amazingrust.com/Experiments/how_to/Pyrophoric_Fe.html https://www.amazingrust.com/Experiments/how_to/Pyrophoric_Fe...
- kortex 6y agoRight. If you increase the surface area or add more oxidizer, iron quite readily burns, see thermic lances, ferrocerium, metal powder explosions etc. But that is different than rusting.
- mikewarot 6y agoA cutting torch for steel is really just an oxy-acetylene torch. Once the flame gets the steel hot enough, you cut back the acetylene, and the pure oxygen burns the steel away. It's a surprisingly effect method of cutting.
- srean 6y agoRight. If a reaction were to be endothermic would we have called it combustion in the first place ? Implied in the name there is this notion that the reagents are looking for an excuse to combust, a release of bottled potential, this in turn implies this has to be an energy producing reaction rather than one where the reagents need to be coerced into reacting by providing external energy
- avereveard 6y ago> rather than one where the reagents need to be coerced into reacting by providing external energy being endothermic or exothermic and activation energy are orthogonal. as a matter of fact, burning wood with air is exothermic, but you don't see thees spontaneously burning until some activation energy is provided. heck, it's not even a given that all exothermic reaction are self sustaining, there's plenty that will go on producing small quantity of heat but will required external energy to sustain the reaction; sometimes it's even the same reaction but in a different environment with a different chemistry or average temperature.
- kortex 6y agoYes, kinda, with a few small exceptions. Exothermy and being thermodynamically spontaneous are strongly correlated, but you can have endothermic spontaneous reactions, such as dissolving urea in water in those instant ice packs. You can also drive reactions by removing the end products in lieu of providing external energy.