# Does oxyhydrogen require the presence of water to ignite?

I recently read a short story (fiction) where a major plot element was based on the expectation that a mixture of oxygen and hydrogen will not ignite unless some amount of water is present to get the reaction started. Wikipedia has no mention of this property, and I couldn't find any other claims one way or another.

Quote from the story: "Hydrogen and oxygen will not unite in the total absence of water"

Is this true?

TL;DR: No.

Campbell is known for being a "hard sci-fi" writer, so one can assume the facts described in the story don't contradict with the state of science at that time. From the context of the book ("The Tenth World", Dec 1937) the action takes place on a transplutonian planet where rivers of liquid hydrogen wash shores of solid oxygen. Assuming the pressure close to atmospheric, this suggests the temperature range between 14 K and 20 K (LH2). And a proton gun is used to initiate the reaction (explosion) between the elements.

The most recent work of the same year was Kassel's detailed research on kinetics of hydrogen ignition (Jul 1937) [1]. At that time the temperature margins for the explosive region haven't been drawn precisely yet:

The effect of temperature also is rather uncertain. It seems that when the upper and lower limits are far apart, the lower limit decreases only slightly as the temperature is increased, but that for low temperatures, where the two limits come together, the effect is considerably greater.

However, it was shown that this is a chain reaction occurring in the gas phase:

The ignition region is unquestionably due to a chain reaction. The chains ordinarily start on the walls, but a few originate in the gas [...] Branching occurs in the gas. The chains may be broken either by a triple collision in the gas, or by diffusion to the wall. Ignition takes place, according to the simple theory, when the rate of branching is greater than the rate of breaking.

Nothing implies that water promotes the reaction. The mechanism has been significantly improved since [2] and explosion limits were precisely detected:

E.g. for an explosion to occur, one must've supply a tremendous amount of energy via proton gun (whatever this is) to locally increase the temperature of the environment, vaporize liquid hydrogen and solid oxygen and heat them both up to at least 400 °C.

Also, according to modern views, the reaction mechanism can be written in the following simplified form (there are many more stages, only the main chain is shown):

\begin{align} \ce{H2 &→[Δ/hν] 2H^.}\\ \ce{H^. + O2 &→ HO^. + O^.}\\ \ce{HO^. + H2 &→ H2O + H^.}\\ \ce{O^. + H2 &→ HO^. + H^.} \end{align}

Rate-limiting stage is the dissociation of hydrogen molecule. A single H atom is then responsible for generation of hundreds of thousands of water molecules. There is no evidence that presence of water catalyses or somehow promotes the chain reaction. The reaction, however, can be catalyzed by transition metals such as dispersed Pt (see also Döbereiner's lamp).

To sum it up, it seems like Campbell couldn't know for sure the exact mechanism for hydrogen burning at that time, and as it later turned out, water doesn't marginally affect it. Probably he just decided to use the concept of seed crystal for water formation.

### References

1. Kassel, L. S. The Mechanism of the Combustion of Hydrogen. Chemical Reviews 1937, 21 (2), 331–345. https://doi.org/10.1021/cr60069a010.
2. Das, L. Hydrogen-Oxygen Reaction Mechanism and Its Implication to Hydrogen Engine Combustion. International Journal of Hydrogen Energy 1996, 21 (8), 703–715. https://doi.org/10.1016/0360-3199(95)00138-7.
• Plus 1. But OP refer to ignition not to ignition leading to explosion (though this is indeed the scenario sketched by the novel). Burning would happen anyway presumably even out the composition or P,T limits for explosion (as per the question). – Alchimista Mar 3 at 15:19