Calcium carbonate (CaCO3) is heated to form calcium carbide (CaC2), which reacts with water to produce acetylene gas (C2H2). Acetylene gas is then used to synthesize ethylene (C2H4) through a process called hydrochlorination, where acetylene is reacted with hydrogen chloride (HCl) to form vinyl chloride (C2H3Cl) which is then hydrolyzed to form ethylene (C2H4). Ethylene can further be reacted with hydrogen chloride to form ethyl chloride (C2H5Cl).