A chemical reaction could be caused by host of causes. The commonest cause of a chemical reaction is when the heat application adds to different chemicals which in turn cause a reaction.
An example of this kind of reaction is visible while cooking food. Another cause of a chemical reaction is when an acid is added to a base. One more cause of chemical reaction is the total balancing of the chemical levels within each other. It is known as the natural PH level among the chemists.
A chemical reaction takes place because it tends to reach the lowest energy content
that’s why the metal corroded by time , and the iron rusts
because these metals are extracted by doing an effort on it like heating in electric furnace , so they tend to back to their origin low energy state.