How do chemical reactions rearrange atoms into new substances?

In a chemical reaction, substances known as reactants are converted into different substances called products by rearranging their constituent atoms.12

This process is fundamentally driven by changes in chemical bonding:

• Breaking Bonds: To initiate the rearrangement, existing bonds between atoms in the reactant molecules must be broken. This step requires an input of energy.13
• Forming New Bonds: The freed atoms or molecular fragments are then reassembled into new configurations. As these new chemical bonds form, energy is evolved (released).1

The net result of these combined processes is the creation of products with chemical properties distinct from the original reactants. Throughout these transformations, the total mass remains constant, a principle known as the conservation of mass, which dictates that matter is neither created nor destroyed during the reaction. Unlike physical changes—such as a change in state—chemical reactions alter the chemical identity of the substances involved.142