I’m curious about the principles behind heat release and absorption in chemical reactions. What determines whether a reaction releases heat (exothermic) or absorbs heat (endothermic)? Is it related to specific types of bonds breaking or forming, or are there other factors involved?
In: Chemistry
Yes they bonds store energy. Just like a compressed spring that makes something move quickly when released. Quickly moving molecules IS heat.
Now some reactions replace somewhat compressed springs with very compressed springs, that is only possible when energy is added from the outside, that’s endothermic.
Usually most systems want to be in balance, so they strife for the most relaxed way to arrange their springs.
It mostly depends on which bonds form and which bonds break.
Burning hydrogen and oxygen to water can seen as a three-step process:
* Split two hydrogen molecules apart into four hydrogen atoms. Hydrogen attracts other hydrogen, so splitting them needs a bit of energy.
* Split one oxygen molecule into two oxygen atoms. Oxygen attracts other oxygen, so splitting it needs a bit of energy.
* Let each oxygen atom react with two hydrogen atoms. Hydrogen and oxygen strongly attract each other, so this step releases a lot of energy. Some of that energy ends up splitting more hydrogen and oxygen (which continues the reaction), the rest ends up as heat.
It’s a bit like rearranging magnets – some arrangements have the magnets all aligned nicely, going from a more chaotic arrangement to this ordered layout will make the magnets snap together quickly, releasing some energy as heat (and sound).
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