Ethylene has the chemical formula C2H4 and CAS number 74-85-1. At ambient temperature and pressure, it is a colorless, flammable gas with a faint characteristic hydrocarbon odor. It is soluble in alcohol and diethyl ether but only slightly soluble in water and is chemically reactive. It has a freezing point of -169.4°C, a boiling point of -103.71°C, a relative density of 0.5699 at -103.8°C, a refractive index of 1.363, a flash point below -66.9°C, a critical temperature of 9.90°C, a critical pressure of 4.95 MPa, a critical density of 0.227 kg/L, an expansion coefficient of 0.006894 at -17.8°C, and a latent heat of vaporization of 495.98 J/g at the boiling point. Ethylene is one of the most fundamental petrochemical feedstocks and is widely used to manufacture plastics such as polyethylene (PE), high-density polyethylene (HDPE), polystyrene (PS), and polyvinyl chloride (PVC).