Kinetics of the reaction: H+HI→H2+I at 298 K and very low pressures

✍ Scribed by Savvas Vasileiadis; Sidney W. Benson

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 214 KB
• Volume: 29
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/(sici)1097-4601(1997)29:12<915::aid-kin3>3.0.co;2-p

✦ Synopsis

The reaction was studied at 298 K and millitorr pressures em-1 H ϩ HI : H ϩ I 2 ploying the "Very Low Pressure Reactor" (VLPR) kinetic technique. H-atoms were generated by dissociating H 2 molecules (of a H 2 /Ar mixture) in a microwave discharge cavity that preceded the very low pressure well-mixed reaction vessel. Quadrupole mass spectrometry was used to analyze molecules and atoms. The mass signal intensities of I and HI were measured at both 20 and ionizing potentials while those of H and H 2 were measured at due 40 eV 40 eV to the very weak signal of these species at lower ionization potentials. Three different exit flow orifices were utilized in the reported VLPR experiments of about 2, 3, and inner diameter 5 mm to vary the species concentration under steady-state reaction conditions. A rate constant of was determined for the forward reaction at Ϫ11 3 k ϭ (2.1 Ϯ 0.2) ϫ 10 cm /molecule.s 298 K, 1 which lies between the two previously reported values directly measured at Satisfactory 298 K. mass balance relations were obtained for the iodine atoms (from the HI and I species) which were better than 90% for most of the experiments. The value of the reported rate constant (k 1 ) is 14.3% higher than the value measured by Umemoto et al. [6], and 33.3% lower than the value measured by Lorenz et al. [4]. Based on this comparison, the activation energy E 1 of the forward reaction probably lies between those two previously reported values of 580 and Transition State Calculations of A 1 and A 2 for the reaction of are 2 720 cal/mol. H ϩ I : HI ϩ I 2 in good agreement with the data on both reactions and suggest an activation energy of about for E 2 .