Chemical change

A chemical change is a change between two or more reactants that results in the formation of (a) new chemical substance(s). At the molecular level, chemical change involves the creation or destruction of bonds between atoms. The following changes are chemical:

• iron rusting (iron oxide forms)
• gasoline-burning (water vapor and carbon dioxide form)
• eggs cooking (fluid protein molecules uncoil and crosslink to form a network)
• bread rising (yeast converts carbohydrates into carbon dioxide gas)
• milk souring (sour-tasting lactic acid is produced)
• suntanning (vitamin D and melanin is produced)

When a chemical change happens, something new must be made or something original must have been destroyed. When you burn paper, the paper is burnt and ash, smoke, and the fire is produced. Also, the change that you created must not be able to change back without another chemical change, or else it is a physical change. When a chemical change is made, the chemical components of the substance is changed or rearranged. The mass of the reactants must be the same as the mass of the product.