[Aerandir]

I know that Cl₂ + H₂ => 2HCl, and I know that this reaction is exothermic. My question is, how exothermic? In other words, how hot does it get? Does this reaction require a spark to get going?

[Borek]

My question is, how exothermic? In other words, how hot does it get?

1327.3

Question as posted doesn't make much sense. You can't ask "how hot it gets" without giving more details. What you can easily check will be ΔH for the reaction, but the final temperature is a function of initial temp and pressure, whether reaction takes place in constant pressure or volume, whether it is adiabatic and so on.

And yes, you need some kind of initiation to start the reaction. Spark or even a photographic flash will do.

[Aerandir]

whoops.
thanks for the info! 

[ajkoer]

Hi:

You may be referring to what in one of my sources is called "chlorine detonating gas" flame, from the combustion of H2 in Cl2.

The temperature of the chlorine detonating gas flame is stated to be about 2,200 C.

Hot, but not as hot as an Atomic Hydrogen (H2 passed through an electric arc, which releases the large required cleavage energy upon recombining) which is put at over 4,000 C!

Now, an idea I had (I let someone else do the work and perhaps mention me) is that since Atomic H2 has a half-life of a few tenths of a second, it is possible to combine the atomic hydrogen in a second region per my source ("Concise Encyclopedia Chemistry" by deGruyter). So what if the 2nd region contained Cl2? If the torch temperatures were additive, we are talking over 6,000 C for an "Atomic H2 Chlorine Detonating Flame"!!!

I have not checked if someone has already invented it, but sounds like a hot idea (pun intended)!

[ajkoer]

AJKOER here again.

On my idea of combining Atomic H2 with Cl2, the reaction would still be around 4,000 C as the heat of an ordinary H2 + O2 is at most 2,300 C, which is hotter than the ordinary H2 + Cl2 at 2,200 C. So, no net temperature gain still around 4,000 C.

However, did come across a reference on Atomic Chlorine (I would guess by the same electric arc process as Atomic Hydrogen). So combining an Atomic H2 with Atomic Cl2 in the 2nd region could be extremely hot (over 6,000?, just a guess).