We teach (ad infinitum....) that a more reactive halogen will displace a lesser halogen from a compound. And yes, the halogen is a halide ion in the compound. Now I think about it, it's usually in solutions, so the halide is nominally solvated and surrounded by water (as hydronium ions?).

But how?

Does the halide lose the electron to give a radical, or does the halogen dissociate to radicals, or to ions, or is there an intermediate Cl2- ion, for example? I realise this is several questions, but the major question is unaffected by my speculation. All I have found is the bald statement about displacement and reactivity and the table we always draw.


closed as unclear what you're asking by Jan, Buttonwood, airhuff, paracetamol, Todd Minehardt Jun 23 '17 at 17:23

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    $\begingroup$ Can you give an example of the type of compound undergoing this displacement? It seems that you're talking about inorganics, but I can't tell for sure. $\endgroup$ – jerepierre Jun 22 '17 at 17:58

I'm guessing your talking about the halogen displacement reactions:

$$\ce{2NaBr + Cl2 -> Br2 + 2NaCl}$$

which is a redox reaction:

  • $\ce{2 Br- -> Br2 + 2 e-}$, bromine loses electrons (is oxidised)
  • $\ce{Cl2 + 2e- -> 2 Cl-}$, chlorine gains electrons (is reduced).

For more detail look in to the redox potentials, this explains what will reduce what.

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    $\begingroup$ Welcome to ChemSE. For future reference, it may be interesting for you to familiarise yourself with the formatting tools made accessible, which are pretty helpful for chemical equations (and other aspects, too): chemistry.meta.stackexchange.com/questions/86/… and mhchem.github.io/MathJax-mhchem. $\endgroup$ – Buttonwood Jun 22 '17 at 22:09
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    $\begingroup$ This doesn't answer the question, which is about mechanism of this redox reaction. $\endgroup$ – Mithoron Jun 22 '17 at 22:17

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