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I am trying to write a balanced equation for the above mentioned reaction but having some trouble figuring it out. So far, I have:

$$\ce{([C6H4N3O2]+ Cl^{-}) + H2SO4 + H2O -> C6H5NO3 + N2 + ?}$$

How do I "incorporate" sulfuric acid and water into the reaction? Thanks for any help.

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The sulfuric acid is not consumed in the reaction pathway to product, so there's no reason for it to appear in the equation for the reaction. Therefor, the overall equation for the reaction is $$\ce{([C6H4N3O2]+ Cl^{-}) + H2O -> C6H5NO3 + N2 + HCl}$$

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  • $\begingroup$ I have no problem with your answer, but I'm just curious, how is sulfuric acid catalytic here? My understanding has always been that its only role is to acidify the solution from the start, so as to avoid azo-coupling side reactions. $\endgroup$ – Greg E. Jun 10 '14 at 3:20
  • $\begingroup$ That's what I recalled, but I couldn't find a reference to support sulfuric acid having a large effect on the rate of diazonium salt decomposition. I'll modify my answer accordingly. Thanks! $\endgroup$ – ron Jun 10 '14 at 13:10
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The water is the source of the hydroxyl ($\ce{-OH}$) group in the phenol, which accounts for one oxygen and one hydrogen. The other hydrogen is ultimately abstracted, probably by a second molecule of water to form $\ce{H3O+}$. The simplest way of representing this, however, is to simply write $\ce{HCl}$ on the product side, though it's tacitly understood that it's unlikely to actually exist undissociated in any significant quantity.

As for the $\ce{H2SO4}$, I'm fairly certain its only purpose is to maintain the acidity of the solution, with the aim of avoiding azo-coupling side reactions. (Although, with a para-substituted deactivating nitro group, this is probably not much of a concern.)

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