The equilibrium constant for N2O5 NO2+ NO3: Absolute determination by direct measurement from 243 to 397 K

Article abstract of DOI:10.1063/1.454679

The equilibrium constant for N2O5 <*> NO2 + NO3 , has been determined through direct concentration measurements of N2O5, NO2, and NO3 in a temperature controlled long path cell, using absorption spectroscopy in the infrared and visible regions from 243 to 397 K.The results give K_1C = 1.30 X 10²⁶ exp(- 21490/RT) molecules cm^-3 with an estimated overall uncertainty of 30percent at the 95percent confidence level.This results in an equilibrium constant near room temperature approximately one-half that of previously accepted values.Using the temperature dependence of the equilibrium constant and new data for the enthalpy of formation of gaseous N2O5 yields an enthalpy of formation for N03 of 15.39 +/- 0.72 kcal mol^-1.In additional experiments the temperature dependent first order decay rates of N2O5 were determined from which a value for the product of the equilibrium constant (K_1C) and the rate constant for reaction (2) : NO2 + NO3 -> NO + NO2 + O2 was obtained for temperatures from 298 to 396 K:K₁k₂ = 1.23 X 10₁₃ exp(- 24 300/RT) s^-1.When this is combined with the equilibrium constant of the present study the following expression is obtained for k₂:9.5 X 10^-14 exp(- 2810/RT) cm³ molecule^-1 s^-1.

Full text of DOI:10.1063/1.454679

The equilibrium constant for N2O5NO2+NO3: Absolute determination by direct
measurement from 243 to 397 K
C. A. Cantrell, J. A. Davidson, A. H. McDaniel, R. E. Shetter, and J. G. Calvert
Citation: The Journal of Chemical Physics 88, 4997 (1988); doi: 10.1063/1.454679
View online: http://dx.doi.org/10.1063/1.454679
View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/88/8?ver=pdfcov
Published by the AIP Publishing
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