Decomposition Reaction. Graham Bell. Edison. Charles Babbage. Albert Einstein. Newton. Master Scientist. My Science World. Eye Scanner, Lock System. Match Found. A reaction in which a compound splits up into two or more simpler substances is known as a decomposition reaction. Let us take an example. Ferrous Sulfate. Color of ferrous sulfate crystals is green. Heat the test tube. The color of ferrous sulfate crystals first changes to white as it loses molecules of water of crystallization. Ferrous sulfate changes to reddish brown due to the formation of ferric oxide. Sulfur dioxide and sulfur trioxide gases are also released in this reaction. They have a pungent and rotten smell due to the burning of sulfur. These gases are toxic. They should not be inhaled. Ferrous sulfate splits up into 3 simpler substances, that is, ferric oxide, sulfur dioxide and sulfur trioxide. The End.