The reaction involved 1 mol of oxygen and 2 mol of hydrogen. prove that atoms are preserved in chemical reactions.

As a result of a chemical reaction, all chemical bonds are broken in substances.

Remembering the law of conservation of energy, that nothing arises from anywhere and does not disappear without a trace, we find that in the reaction of 1 mole of oxygen and 2 mole of hydrogen, 2 moles of oxygen atoms (O2) and one mole of hydrogen atoms (H) will be formed, since there is a complete rearrangement of all atoms in substances.