Is burning of paper a chemical reaction. Yes through heat you are converting it from paper (cellulose) to gaseous water vapor and CO2 and traces of other chemicals, and changing the composition of the remaining paper i.e turning it black - unburned carbon.Chemical changes occur when a substance combines with another to form a new substance, called synthesis or, alternatively, decomposes into two or more different substances. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. Some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. Understanding chemical changes is a major part of the science of chemistry.