Chemical change is a change in a substance that transforms it into a different substance. Chemical change is distinct from physical change, which is a change in the physical features of an object without a corresponding change in substance. Heat, combustion and mixture of chemicals can all cause chemical changes.
Chemical changes affect a substance by interactions among molecules, particularly through atomic bonds joining or separating. Whereas some chemical changes happen very rapidly, others take place slowly. The result may be a compound with the same number atoms that are rearranged in a different order. Fructose, glucose and galactose all have the same number of atoms, but chemical changes cause different arrangements and thus different substances. In addition, whereas some chemical changes are visible, others take place with no apparent change, such as in the case of hydrogen peroxide changing into water. Whether the changes are readily apparent or not, most chemical changes leave behind evidence of the process through odor or other indicators such as sound, light, gas, heat or changes in color.
An additional example of chemical change is burning a sugar cube. Fire causes sugar and oxygen to undergo a chemical interaction where oxygen causes the chemical bonds to break down.