I don't just mean reactions that require heat to proceed, storing surplus energy in chemical bonds. I wonder about strongly endothermic reactions that suck heat out of environment.
You take some substance A (e.g. Ammonium Nitrate), and some substance B (e.g. water), both at room temperature. You mix them together in a beaker which is room temperature, all performed in room temperature air. As the reaction begins, the two substances binding into substance C, the beaker cools down quite a bit below room temperature.
This is what we observe on macroscopic scale.
I wonder what happens on the microscopic scale - chemical particles, atoms, elementary particles, their energy. Normally entropy would suggest everything would remain in equilibrium but suddenly we have a higher energy concentration within the substance at cost of energy of the environment. It is not easily reversed. What happens that makes particles "want" to bind so much that they specifically "steal energy" from the environment just so that they can react?