Vapor Pressure of Antimony by the Torsion-Effusion Method

Abstract

The pressures and mean molecular weights of the vapors over solid antimony (420–550°C) and solid zinc (250–335°C) have been determined by simultaneous measurements by the torsion‐momentum and Knudsen weight loss methods. The torsion measurement was calibrated with mercury at 30° using a mercury vapor pressure of 2.96×10^‐3 mm Hg determined by concurrent weight loss experiments. Zinc vapor is confirmed to be monatomic. The zinc pressure data are represented by logP_mm=(8.741±0.218) — (6630±125) /T giving ΔH₂₉₈° (vap)=30.73±0.57 and 31.18±0.12 kcal/mole by the second law and third law of thermodynamics, respectively, in excellent agreement with previously reported results. The vapor over solid antimony is all Sb₄ molecules within experimental error. Least‐squares analysis of the antimony data yields logP_mm=(10.571±0.090) — (10 300±68) /T, pressures 10%‐40% lower than those previously reported. The heat of vaporization of Sb₄(g) at 298.16°K is 49.83±0.31 kcal/mole by the second law and 49.45±0.09 by the third law of thermodynamics. This thermodynamic consistency and the agreement of the zinc results with accepted measurements indicate that the antimony pressures presented should be preferable to those previously reported.