The combination of hydrogen and oxygen in a silver vessel

Abstract

As is now well known, reaction chains may play a prominent part in the combination of hydrogen and oxygen. The region of temperature in which the chain processes are important is limited. Below it, the combination takes place exclusively on the walls of the vessel, while above it the reaction is so rapid that it ceases to be isothermal in any sense and passes into explosion. In vessels of silica or porcelain the development of a non-explosive reaction in the gas phase occurs between about 540° and 600°C. The characteristics of this reaction are first, a very pronounced dependence of rate upon pressure— for example under some circumstances the rate may vary as the cube of the hydrogen concentration; secondly, sensitiveness to the accelerating influence of inert gases, including steam; and thirdly, an extremely marked increase in rate as the diameter of the vessel is increased. The last two characteristics show that the chains propagating this particular mode of reaction are terminated principally at the wall of the vessel. The action of the walls depends upon the deactivation of active molecules, or more probably upon the destruction in a definite chemical reaction of certain species normally responsible for continuing the chains. As examples of possible reactions we may take the decomposition of hydrogen peroxide, or the recombination of hydrogen atoms or of hydroxyl radicles. All these processes would be very sensitive to surface catalysis. If the vessel wall actively promotes them the rate of the reaction in the gas will be kept small.