Evaluation of the Equilibrium Constant for the N2O4 (g)=2NO2 (g) Reaction at 298.16°K from Light-Transmission Measurements

Abstract

The absorption coefficient of NO2 (g) has been found to be both temperature and pressure dependent for the temperature range 299.71° to 376.52°K and pressures from 2 to 5 cm Hg, for the 5461-Å mercury ``line''. The equilibrium constants for the reaction N2O4 (g)=2NO2 (g), at the temperatures 299.71°, 303.70°, and 308.89°K, have been evaluated by combining precise transmittance measurements for the 5461-Å mercury line with the known vapor pressures of solid N2O4. ΔG°298.16 for the above change in state has been found to be 1.151±0.004 kcal/mole, which, when combined with the known value of ΔS°298.16, gives ΔH°298.16=13.640±0.100 kcal/mole.

The Effect of Diffusion Due to a Temperature Gradient on the Measurement of the N2O4-NO2 Equilibrium Constant

“…Examination of the table shows that the effect of the steady state diffusion on the results can be pronounced, and one wonders how it was possible for Harris and Churney (6) to obtain good values. The authors determined the absorbance coefficient of N02 by back-calculation using known values of Kp at three different temperatures.…”

“…It depends parametrically on the force law between the molecules. As a first approximation, a can be estimated from (18) a -105 M2-Mx a 118 M2 + Mx kT (6) where M\ and M2 are the molecular weights of the lighter and heavier components.…”

“…This design was adopted by Wettack (1) and, in a slightly modified version, subsequently used in our physical chemistry laboratory. Convenient and simple, this approach has nevertheless one potential source of error that was not discussed in any of the two original papers (1,6). This is due to the effect of diffusion caused by the temperature gradient in the system.…”

A spectroscopic study of the nitrogen dioxide-dinitrogen tetroxide system by the infrared absorption technique

“…Using two cells of different lengths, the N02 absorbances at a given frequency vo are equal through the two cells when (Ano2(*o))i = aN02(ro)(PN02)i£i = aN02 (Po) (p N02) 2-^2 = ( 02( ))2 (5) where the subscript 1 refers to the first cell and subscript 2 refers to the second cell. From eq 5 (PN02)i¿1 = (PN02)2¿2 (6) When this condition applies, the absorbances in the two cells are equal.…”

New measurements of the NO2 absorption cross section in the 440‐ to 460‐nm region and estimates of the NO2‐N2O4 equilibrium constant

“…Estimates of Kp have been obtained also by measuring spectroscopically the partial pressure of NO2 and by assuming that the absorption features of the two gases do not overlap in the wavelength region considered. Jacob [1959] and Dunn et al [1962], by measurements of the IR spectra of the equilibrium mixture of NO2 and N20 4 at high temperatures and Harris and Churney [1967] by the optical absorption at 546.1 nm at different temperatures between 299 and 370 K, deduced the concentration and the partial pressure of NO2. A formula for the equilibrium constant was obtained by Vosper [1970] from measurements of the absorption spectrum of the equilibrium mixture in the region 400-500 nm at temperatures between 233 and 273 K. The calculations by Powell and Adams [1978] agree within experimental errors with the results by Giaque and Kemp [1938] and within about 4% with those by Chao et al [1974].…”