A chemical reaction involves the rearrangement of atoms and molecules to form new substances with different chemical properties. Evaporation, dissolution, and storing gas under pressure are physical processes where the substance's chemical composition remains unchanged, only its state or distribution changes. Burning (combustion) is a chemical process where a substance reacts rapidly with oxygen, typically producing heat and light and forming new chemical compounds. When magnesium burns in air, it reacts with oxygen and nitrogen to form magnesium oxide and magnesium nitride, respectively.