The Fourth Edition to the NIST-JANAF Thermochemical Tables has been assembled under the sponsorship of the Standard Reference Data Program at the National Institute of Standards and Technology. It contains tables of recommended temperature-dependent values for the standard enthalpy of formation, Gibbs (free) energy of formation, the logarithm of the equilibrium constant of formation, the heat capacity, entropy, enthalpy, and Gibbs energy function for 48 elements and many of their compounds.