The Reaction of Hydrogen with Oxygen

Few reactions have been studied as extensively as the classical reaction of hydrogen and oxygen. Because of its relative chemical simplicity, it has served as a prototype and proving ground for theories of branching chain explosions. 

At temperatures below about 400° C the reaction is predominantly heterogeneous with a rate which varies considerably depending on the nature of the surface, the previous history, and the extent, that is, the S/V ratio of the reaction vessel. At pressures below 20 mm Hg and in vessels whose walls have been coated by KCl, the rate of reaction is immeasurably slow in this temperature region. 

Below the first explosion limit the rate of reaction seems to be negligibly slow. Above the second explosion limit, studies of the rate of the normal reaction have shown considerable irreproducibility among different laboratories and even in the same laboratory. The rates are remarkably sensitive 

Explosion limits of a stoichiometric mixture of IE + O2 in a KCl-coatcd spherical vessel (7.4 c.in diameter). Explosive region lies in shaded region to right of (jritical boundary first limit is somewhat erratic . Dashed parts of curve represent extrapolations. 

The only serious difficulties with the use of these data lie in the uncertainties in the for HO and, particularly, HO2. 

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The calorimeter in figure 7.10 was electrically calibrated [54,99] by using the heater O. Flame calorimeters are, however, most frequently calibrated on the basis of the reaction of hydrogen with oxygen, which has been recommended for this purpose by IUPAC [39]. 

The reaction of hydrogen with oxygen runs according to a branching chain mechanism ... 

In the reaction of hydrogen with oxygen equilibrium is approached from the side of excess atoms and radicals, and the amount of reaction heat released asymptotically and gradually approaches the thermodynamic limit. 

Write the unbalanced equation using the correct chemical formula for each reactant and product. In the reaction of hydrogen with oxygen to yield water, for example, we begin by writing ... 

Certain chain reactions involve steps which generate more free radicals than they consume. This is called chain branching. The inherent self-acceleration may or may not outrun termination. If it does, a detonation results. A classical example is the reaction of hydrogen with oxygen. 

The reaction products from the fuel must be gaseous so that they can be directly vented to the air. This eliminates the requirement for hardware to collect, store and return the spent solid or liquid reaction products. The product of the reaction of hydrogen with oxygen, from the air, is water. There is no carbon so no un-bumed hydrocarbons or toxic carbon monoxide is produced. All fossil fuels contain some amount of sulfur compounds. These are converted to sulfur dioxide when the fuel is burned. Most processes under consideration for the production of hydrogen are free from sulfur or any other harmful contaminants. Thus, unlike fossil fuel hydrocarbons, hydrogen combustion products will not be contaminated with sulfur compounds. 

The negative sign indicates that heat is evolved in the reaction of hydrogen with oxygen. 

Notice that each of these reactions involves oxygen, so each can be classified as an oxidation-reduction reaction. The first two reactions are also commonly called combustion reactions because they produce flames. The reaction of hydrogen with oxygen to produce water, then, can be classified three ways as an oxidation-reduction reaction, as a combustion reaction, and as a synthesis reaction. 

The reaction of hydrogen with oxygen is highly exothermic and occurs rapidly once it starts. It can occur with explosive violence, as demonstrated by the explosions of the German airship Hindenburg in 1937 (V FIGURE 5.15) and the U.S. space shuttle Challenger in 1986. 

We use chemical formulas to identify the specific reactants and products. The physical states of the compounds are often designated (s) indicates a solid, ( ) a liquid, (g) a gas, and (aq) a substance dissolved in water. We can write the reaction of hydrogen with oxygen, which is often done as a lecture demonstration, as a simple example. 

The reaction of hydrogen with oxygen to form watCT is an example of a reaction that requites the input of energy to get started howevCT, once it does, the reaction is rapid and exothermic. 

The reaction of hydrogen with oxygen produces water. 

A process to produce hydrogen peroxide directly from the elements has been of interest for many years. The problem with the direct synthesis process is that, in terms of thermodynamics, the reaction of hydrogen with oxygen favors production of water. It had been recognized for some time that a finely dispersed catalyst is beneficial in promoting... 

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