The Differences in the Vapor Pressures, Heats of Vaporization, and Triple Points of Nitrogen (14) and Nitrogen (15) and of Ammonia and Trideuteroammonia

Abstract

The differences in the vapor pressures of natural nitrogen and samples containing 34.6 percent nitrogen‐15 were measured by a differential method and were found to be given by log P₁/P₂=(0.2474/T)−0.001994 where 1 refers to the natural nitrogen and 2 refers to the heavy sample. The difference in the heats of vaporization of the two samples was calculated to be 1.14 calories, that of the heavy sample being higher. The triple point pressures were measured and found to be 9.386 cm of Hg and 9.378 cm of Hg, respectively. From this the difference in the triple points was calculated to be 0.020°K. Assuming that Raoult's law may be used, the ratio of the vapor pressures and the difference in the heats of vaporization of the two pure isotopes, nitrogen‐14 and nitrogen‐15, were found to be $$\begin{array}{c}\log {\mathrm{(P}}_{14}{\mathrm{/P}}_{15}\text{)=(0.7230/T)−0.005822}\\ {\mathrm{\Delta H}}_{\mathrm{vap}\text{\hspace{0.17em}15}}{\mathrm{-\Delta H}}_{\mathrm{vap}\text{\hspace{0.17em}14}}\text{=3.33\hspace{0.17em}}\mathrm{calories}.\end{array}$$ The triple point of the pure nitrogen‐15 was found to be 0.058° higher than that of nitrogen‐14 and the boiling point 0.052° higher. The differences in the vapor pressures of solid natural ammonia and of solid trideuteroammonia containing 98 percent deuterium were measured and found to be given by $$\log {\mathrm{(P}}_{{\mathrm{NH}}_3}{\mathrm{/P}}_{{\mathrm{ND}}_3}\text{)=(49.69/T)−0.1305.}$$ The vapor pressures of the liquid ammonias were found to follow the equation $$\log {\mathrm{(P}}_{{\mathrm{NH}}_3}{\mathrm{/P}}_{{\mathrm{ND}}_3}\text{)=(46.25/T)−0.14003.}$$ These two equations agree at the triple point. The difference in the heats of sublimation was calculated to be 227 calories, while the difference in the heats of vaporization is 212 calories, the values for the trideuteroammonia being higher than those for ammonia. The triple point pressures were found to be 4.557 cm of Hg for ammonia and 4.822 cm of Hg for the trideuteroammonia. This corresponds to triple point temperatures of 195.68°K and 198.79°K, respectively. The boiling point of the trideuteroammonia was found to be 2.37° higher than that of the ammonia.