The kinetics of the interaction of nitrous oxide and hydrogen

Of the three related reactions 2N2 O = 2N2 + O2 [1] 2H2 + O2 = 2H2 O [2] N2 O + H2 = N2 + H2 O [3] only the first two have hitherto been studied. The investigation of the kinetic relation of the third to the first two is the object of this paper. In the preceding paper it has been shown that the thermal decomposition of nitrous oxide into its elements is a homogeneous reaction in which practically every pair of nicrous oxide molecules react which collide under the condition that their joint energy exceeds about 58,000 cals, (for 2 gram molecules). This decomposition is uncatalysed by platinum or by rhodium. The combination of hydrogen and oxygen is, on the other hand, a reaction very dependent on catalytic influences. Bodenstein (‘Z. Physikal. Chem.,’ vol. 29, p. 665 (1899)) found that between 482° C. and about 600° C. the combination proceeds exclusively on the walls of a porcelain containing-vessel. Platinum, rhodium, and other metals have long been known to have a very pronounced catalytic action on a mixture of hydrogen and oxygen. Langmuir (‘Trans. Faraday Soc.,’ vol. 17, p. 621 (1922)) has studied the kinetics of the interaction of hydrogen and oxygen on the surface of a platinum wire, and finds that between 300° and 600° abs. the rate of combination is approximately proportional to the pressure of the oxygen and inversely to that of the hydrogen. There is now abundant evidence that catalytic reactions occur within a layer of adsorbed gas not more than a molecule or so deep, in immediate contact with the surface, and the interpretation of Langmuir’s results is that between 300° and 600° abs. the surface of the platinum is nearly completely covered with a layer of hydrogen and that reaction occurs when oxygen molecules enter gaps in this layer, the number of free spaces being easily shown to be inversely proportional to the pressure of the hydrogen. Turning now from the reactions [1] and [2] to the related reaction [3], the following questions present themselves, namely:— (a ) whether nitrous oxide and hydrogen undergo a homogeneous bimolecular interaction at temperatures below that at which [1] takes place; (b ) whether hydrogen and nitrous oxide interact catalytically on the surface of platinum. On the one hand, platinum becomes covered with a film of hydrogen which is activated for reaction [2], while on the other hand, platinum has no activating effect on nitrous oxide for reaction [1].