The Thermodynamic Properties of Gaseous Sulfur Trioxide

Abstract
The thermodynamic properties of sulfur trioxide in the ideal gas state are calculated from molecular data. To obtain satisfactory agreement with the equilibrium data for the reaction SO2+½O2=SO3, it is necessary to include vibrational anharmonicities, which are somewhat larger than usual because of an accidental degeneracy involving two of the normal frequencies. The standard entropy of SO3(g) at 25°C is 61.2±0.2 E.U., and its standard heat and free energy of formation from the elements are ΔH°298.16=−94.43±0.15 and ΔF°298.16=−88.48±0.20 kcal./mole.
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