[ifuller]

Does anyone know a formula to calculate the approximate time that it would take for two mono-atomic elements (ie. H + H) to form H2. I know that the time will be very short but are we talking microseconds or tenths of a second. Thanks for anyone who can help.

[Borek]

No idea about the formula, but think for a moment. If they are a mile apart, it will take forever. If they are at the distance they are in the molecule, reaction will be almost instant.

Is your question well defined?

[ifuller]

That is a good point that I didn't address. The reason I ask is I am interesting in splitting H2 into H and H and then using those molecules to react with other chemicals. I am trying to figure out if this is possible. Thanks for the input though.

[Kryolith]

Starting from molecular H₂ requires drastic conditions, but you can easily create hydrogen in statu nascendi by the reaction of metals with acid... For what kind of reactions do you need it?

[ifuller]

I am experimenting with reactions in which a reactant combines with hydrogen only under extreme conditions. I am planning on using a heated tungsten filament to split H2 into atomic hydrogen. I then hope to react that atomic hydrogen with the other reactant to create the same products with much lower energy requirements.

[lemonoman]

Like Borek said, it's going to depend on how much H^. you have there.  The number density is what will tell you how long the H^. will last:

Rate constant for the reaction: H + H --> H2

Rate (of formation of H2) = k[H][H]
where [ ] is the number density (molecules/cm³ or mol/L)

k for your reaction can be found at: NIST Kinetics Database
- Just like all rate constants it depends on temperature...but you can make an approximation

Last thing: Be careful, radicals have a tendency to react with lots of stuff