[cabaal]

I'm given the following and asked to predict the reaction:

(2 Cl₂ - H₂O) + Na₂CO₃  ?

I guessed:

(2 Cl₂ - H₂O) + 2Na₂CO₃  NaCl + H₂CO₃

Apparently this isn't correct because H₂CO₃ decomposes as such:

H₂CO₃  H₂O + CO₂

Is there any way to predict the decomposition? Apparently it decomposes because decomposition is energetically favorable, but I'm not given and thermodynamic data and I think that's most likely beyond the scope of what I've been taught. Is it just something that I'm supposed to know?

[cabaal]

I also have another question. Would the following occur or is it a non-reaction?

HCl (aq) + NaI (aq)  NaCl (aq) + HI (aq)

H⁺ + Cl^- + Na⁺ + I^-  Na⁺ + Cl^- + H⁺ + Cl^-

I remember reading that if all ions are spectator ions in a net ionic equation, then the reaction does not occur. But why is this? Wouldn't a reaction have to occur (as shown by the dissociated salt ions in solution after the reaction completes)?

[Borek]

I would say there is no reaction in both cases. Carbonic acid decomposes, but carbonates are quite stable, presence of strong oxidizing agent doesn't matter - there is no reducing agent present.

You have not shown (in the second case) that reaction HAVE to occur. You have juggled the order in which ions are listed (ignoring obvious mistake - transmutation of I^- to Cl^-) but nothing have changed.

[Borek]

It was pointed out to me (thanks AWK) that in fact in the first case something will happen, albeit slowly. Chlorine reacts slowly with water producing HCl and HOCl.

Both acids will react with carbonate, CO₂ will left solution and equilibrium will shift to the right. Final solution will be mixture of NaCl/NaOCl/carbonate (relative amounts depending on the partiall pressure of CO₂ above the solution).