Physical and chemical processes can be classified by the changes occurring on the molecular level. In general, chemical processes involve changes in chemical bonds, while physical processes involve changes only in intermolecular forces.

A few examples of chemical change are digestion of food, burning of coal, rusting, etc. Generally, physical changes do not involve the production of energy. Chemical changes usually involve the production of energy (which can be in the form of heat, light, sound, etc.) In a physical change, no new substance is formed.