Question

what is chemical reaction

Answer 1

a process that involves rearrangement of the molecular or ionic structure of a substance, as distinct from a change in physical form or a nuclear reaction.

Answer 2

Chemical reaction is a process where two or more substances or compounds react to form a totally new compound. It usually modifies the bond between the reactant substances. 

For eg: 2H₂+O₂ = 2H₂O (Formation of water from hydrogen and oxygen)     

Hope this helps.....