Lauren H. answered • 09/15/18
Tutor
4.8
(24)
7 years experience teaching High School Chemistry and Honors Chemistry
Uhhhh...
On a microscopic (molecular) level, the bonds between atoms have potential energy. When these bonds are broken and new, and different bonds are formed, macroscopically, energy is released, exothermic, or it is absorbed, endothermic.
Example: 2H2 + O2 → 2H2O exothermic
2H2O → 2H2 + O2 endothermic
