Answer: A chemical reaction is one in which rearrangement of atoms take place. A chemical reaction is characterized by following changes:
1) Absorption or release of heat. Example: Combustion reaction
[tex]CH_4+2O_2\rightarrow CO_2+2H_2O[/tex]
2) formation of gas bubbles
[tex]Mg+2HCl\rightarrow MgCl_2+H_2(g)[/tex]
3) Formation of precipitate
[tex]2AgNO_3(aq)+Ba(Cl)_2(aq)\rightarrow 2AgCl(s)+Ba(NO_3)_2(aq)[/tex]
4) Change in color
[tex]2Mg+O_2\rightarrow 2MgO[/tex]
Colorless [tex]Mg[/tex] changes to white [tex]MgO[/tex]
