Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula C2H4 or H2C=CH2. It is a colorless flammable gas with a faint "sweet and musky" odor when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds), and the second simplest unsaturated hydrocarbon after acetylene (C2H2).Ethylene is widely used in chemical industry, and its worldwide production (over 109 million tonnes in 2006) exceeds that of any other organic compound.