What mass of this substance must evaporate to freeze 170g of water initially at 25C ? (The heat of fusion of water is 334J/g; the specific heat of water is 4.18J/(gK).) Express the mass in grams to two significant digits. Compounds such as CCl2F2 are known as chlorofluorocarbons, or CFCs. These compounds were once widely used as refrigerants but are now being replaced by compounds that are believed to be less harmful to the environment. The heat of vaporization of CCl2F2 is 289J/g