It happens all the time in a million ways. Like let's take something easy that happens fairyl often in elementary school classes as our first reaction: Baking soda is added to acetic acid (vinegar)

NaHCO3 + HC2H3O2 → NaC2H3O2 + H2O + CO2

Molecular bonds were broken. Nothing impressive. If you want to break it further, you can get electricity to go through that water and it will break the water molecules through electrolysis into Oxygen (O2) and Hydrogen.

If you don' feel like breaking the last mollecular bonds yourself you could release the CO2 in the atmosphere. Plants will probably get some of that CO2 transformed into O2 and sugars through photosynthesis.

At the higher layers of the atmosphere, O2 gets broken down all the time into single Oxygen atoms by UV rays and then recombine with nearby O2 to form O3 (Ozone).

Pretty much any chemical reaction you can think of is just that: breaking apart molecules.