Ammonium sulfate - NIST
Dry, powdered ammonium sulfate may be formed by spraying sulfuric acid into a reaction chamber filled with ammonia gas. The heat of reaction evaporates all water present in the system, forming a powdery salt. Approximately 6000M tons were produced in 1981. Ammonium sulfate also is manufactured from gypsum (CaSO 4 ·2H 2 O).The standard enthalpy of formation of any element in its most stable form is zero by definition. The standard enthalpy of formation of any element in its standard state is zero by definition. For example, although oxygen can exist as ozone (O 3), atomic oxygen (O), and molecular oxygen (O 2), O 2 is the most stable form at 1 atm pressure and 25°C.