Chemical potential energy is a huge focus in every physical chemistry class. This energy comes from the tiny electrical attractions and repulsions inside atoms. Protons in the nucleus pull on the negative electrons zooming around them.
The arrangement of these charged particles determines how much energy is stored. When atoms rearrange during a chemical reaction, their potential energy changes. If the new products have lower potential energy than the starting reactants, energy escapes.
This leftover energy usually flows out into the room as noticeable heat or light. Chemists call these specific reactions that release heat into the surroundings exothermic reactions. On the other hand, some reactions require a constant input of heat to happen.
These endothermic reactions pack that extra heat away as new potential energy. A common student mistake is thinking that breaking chemical bonds releases energy. Breaking chemical bonds actually requires an initial input of energy from the surroundings. Forming new, more stable bonds is what truly releases the stored energy.