Shock Waves in Chemical Kinetics: The Decomposition of N₂O₅ at High Temperatures¹

Abstract

The shuck pyrolysis of N2Os in the presence of excess argon has been studied, thus providing information about the properties and reactions of the nitrate free radical, NO3. The important reactions are: N/O5 N02 + NO3 (A and B), N02 + NO3 -» NO + 02 + N02 (e), NO + NO3 -* 2N02 (f), NO3 + N03 -* 2N02 + 02 (g). In the concentration and temperature range studied ([argon] ~0.0076 mole/1., 450-550°K.), the dissociation reaction is a unimolecular reaction close to its second order low pressure limit, -d[N205]/df = A'[A] [N205], with A' = 1013-7 exp(-16,500 ± 700/i?r)(mole/l.)-1 sec.-1.The equilibrium constant of the dissociation reaction is given by Ac = 104-97 exp( -20,100 ± 1100/l?r)(mole/l.). The rate constants of e and g are given (550-1100°K.) by e = 2.3 X 10s exp( -4400 ± 700/l?r)(mole/l.)-1 sec.-1 and g = 2.6 X 109 exp(-7700 ± 1000/1? T)(mole/l.)-1 sec.-1. On the basis of this and other data, the following thermodynamic quantities are calculated: N2Os = NOa + N03, AH\0ok. = 21,600 cal./mole, ASWr. = 33.6 e.u., Aff°i,,0i (NOa) = 17,100 (±1000) cal./mole, S°m (NO3) = 60 ± 2 e.u. The kinetics of various reactions involving NO3 are reviewed and recommended rate constants and activation energies at 300°K. computed. In general, the present investigation, where N03 was a major constituent whose concentration was directly measured, confirms the results of previous investigations in which NO3 was present at low, undetermined concentrations as a reactive intermediate. (1) Research carried out under contract Nonr-220(01) between the

SEVEN MECHANISMS IN THE PHOTOLYSIS OF NO2 BETWEEN 3100 AND 3700 Å

“…Since ks/kg is the equilibriuill coilstailt for the dissociatioil of nitrogen peiltoxide, k6 call be calculated using the value of lie, reported by Schott and Davidson (25). Thus kGIi,, = 0.44 sec-l is in reasonable agreeinent with the value of 1.0 sec-I reported by Hisatsune, Ogg, and Crawford (23).…”

Analysis of the unimolecular reaction N2O5 + M ⇌ NO2 + NO3 + M

“…A final remark concerns the uncertainty of the values of the dissociation energy of NzO5, and the heats of formation of N20.5 and NO3 a t 0 K. The previously used value of AHYO (N03) of the JANAF tables [18] was based on the N2O5 * NO2 + NO3 equilibrium measurements around 500 K in shock waves from [13] and a third-law analysis. These data are nicely consistent with the remeasurement of K,, near 300 K in [9].…”

“…The reaction was also studied at 450-550 K in shock waves by Schott and Davidson [13]. The reaction was interpreted as being at the low-pressure limit with a rate constant of…”

A spectroscopic study of the equilibrium NO2 + NO3 + M 2 N2O5 + M and the kinetics of the O3/N2O5/NO3/NO2/ air system

“…Smith, Ravishankara, and Wine [lo] 2.06b Perner et al [23] 2.12* 1.27** Burrows, Tyndall, and Moortgat [40] 2.50* 2.82** Cantrell et al [15] 4.44* 5.14** Orlando et al [41] This work 3.73* 3.67** tion of K,, has been carried out by simultaneous spectroscopical measurements of all of the three reactants involved in the equilibrium with the IR and UV/VIS beams probing the same volume of air. The equilibrium was studied in a 480 liter chamber at atmospheric pressure within a small temperature interval around room temperature.…”