The experimental results on the decomposition of hydrazine are re-examined. The assumption is made that a dilute hydrazine toluene .gas mixture at low pressure will not undergo isothermal reaction under the flow conditions experienced in the apparatus axed by Szwarc, bat that there will be a strong effect due to heat transfer in the entrance region of the reactor.
Analysis of the non-isothermal reactor leads to reinterpretation o/ the experimental rate data. The existing, data are found to /awmr a second-order ]ormation for NH~ radicals, rather than a first-order formation. The rate constant is approximately 101~exp(-60 O00 / R T) cm:~ / mole sec. which appears to be the low-pressure value in a qmlsi-unimolecular rate process.
THE application of laminar-flame theory to the gaseous hydrazine flame involves the use of a chain mechanism ~. This chain mechanism must be of the second-order overall, to account for the experimental facts concerning flame speed, activation energy, and pressure dependence below one atmosphere.
The chain mechanism which fulfils the necessary requirements is found to have a quasi-unimolecular initiation process: that is, the propagating NH., radicals are formed in a Hinshelwood-Lindemann mechanism (secondorder at low pressures). The flame theory, with the use of this mechanism, permits an estimate of the rate of activation of hydrazine, which is bimolecular.
The motivation for the present paper lies in the fact that the experimental data of Szwarc on hydrazine decomposition in a heated tubular reactor ~ were interpreted to indicate a simple first-order formation of NH2 radicals at low pressures, rather than a second-order formation such as that which seems to be required by flame theory, A closer inspection of Szwarc's data was worthwhile, to determine whether a second-order formation rate for NH, could be established from the data.
The basis of Szwarc's analysis is as follows. If the hydrazine decomposition is assumed to take place in an isothermal reactor, then the rate data favour the first-order NH~ formation. However, a slight dependence of the specific rate constant on the absolute pressure was noted (tending to support second-order NH~ formation), but was dismissed as not significant. The present analysis, using the same experimental data, assumes that the conditions in the tubular reactor are probably isothermal only in the downstream portion and are non-isothermal near the entrance. The results definitely indicate a second-order NH, formation; thus, the experimental kinetic data of Szwarc become consistent with the results of flame data.