In chemical reactions, atoms rearrenge to form products... During chemical change atoms arrange and form new bonds. The new bonds are form to make the products. Chemical reactions occur when different atoms and molecules combine together and spit apart. For example, if Carbon (C) is burnt in Oxygen (O2) to form Carbon Dioxide, a Chemical Reaction occurs. So, during chemical reactions, new product atoms are not created, and old reactant atoms are not destroyed.