A photometric study of the N2O4-NO2 equilibrium. A physical chemistry experiment

Abstract

This study of the N2O4-NO2 equilibrium allows the student to measure several thermodynamic quantities on a gas phase equilibrium and provides extensive laboratory experience in physical chemistry.

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

“…The diffusion flow or current J of a substance in a mixture is the amount of this substance passing perpendicularly through a reference surface of unit area per unit time. If r is the distance coordinate chosen perpendicular to the reference surface and c is the concentration of the diffusing substance, Fick's (8) first law of diffusion may be stated in the form J = -D^ ( 1) ar where D is the coefficient of diffusion for the substance under consideration with dimensions cm2 s_1.…”

“…The apparatus used in our physical chemistry laboratory is shown schematically in Figure 1. The experimental setup in this experiment is an adaptation of that used by Wettack (1).…”

“…The work of Harris and Churney (.£>) was used as a major source of inspiration for a subsequent paper by Wettack (1). Here again, the situation was saved by using known values of Kv to determine the values of the absorbance coefficients.…”

“…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.…”

The complex refractive index .cxa.n(.sigma.,T,.rho.) of NO2/N2O4 in the visible and static dipole polarizability of N2O4

“…Kp with different techniques nowadays is a familiar experiment in a student's laboratory course in experimental physical chemistry. 17,18 Nevertheless, it is very interesting to obtain Kp from our data of the temperature and pressure dependence of the complex refractive index h(a0) recorded at 00. However, because of the limited temperature range and therefore small mole fraction range covered in our experiments (see Figure 6), the results are expected to be of limited value.…”