The second limit of hydrogen + carbon monoxide + oxygen mixtures

Previous studies by Buckler and Norrish of the second limit of CO and O2 mixtures containing small amounts (0.25–10%) of H2 have been used to obtain the velocity constant of the reaction These estimates of k33 = 3.9 × 108 and 3.5 × 108 liter2 mole−2 sec−1 (M H2) at 500° and 560°C, respectively, have been combined with other estimates over the range 300°–3500°K to give k33 = 3.0 × 108 exp (−3000/RT) for M Ar; the considerable scatter in the available points does not encourage any great confidence in this expression and may be attributed at least partly to the different molecules used as M by different workers. For KCl-coated and CsCl-coated vessels at 540°C, studies of the second limit of H2 + O2 mixtures, to which CO has been added, have indicated that with both the surfaces, the effect of CO on the limit is masked by changes in the surface nature. In the case of CsCl, the results have enabled a lower limit of about 0.6 to be obtained for the efficiency of CO relative to H2 in the reaction Use of a computer treatment to interpret the second limit of CO + H2 + O2 mixtures in aged boric-acid-coated vessels at 500°C gives a value of mCO = 0.74 ± 0.04 together with an estimate of k32 (H + CO + M″ = HCO + M″)/k4 = 0.022 ± 0.003, which leads to k32 = 2.3 × 108 liter2 mole−2 sec−1 (M H2) at 500°C.