Question

what is the net ionic for these following balanced equations:

2(NH4)3PO4(aq) + 3Ba(OH)2(aq) -> Ba(PO4)2(s) + 6H2O(l) + 6NH3(g)

2HNO3(aq) + K2CO3(aq) -> H2O(l) + CO2(g) +2KNO3

NaF(aq) + HCl(aq) -> NaCl(aq) + HF(aq)

Answer 1

Reactions go to completion for one of just a few reasons.
1. A ppt (insoluble material) is formed. You need to know the solubility rules to know what is soluble and what isn't. Here is a simplified table.
http://en.wikipedia.org/wiki/Solubility_chart

2. A gas is formed. (H2, O2, Cl2, F2, N2, CO2, SO2, NO2 are few common ones).

3. A slightly ionized substance (weak acid/weak base/water) are formed.
4. Redox reaction.

If one of these doesn't happen generally there is no reaction. To write the net ionic equation, remember that if it is a gas, insoluble, or weak electrolyte formed, you write that as the molecule. If none of those, the material isn't listed. For example, for #1, Ba3(PO4)2 is insoluble (rule 1) above and the net ionic equation is
2PO4^3-(aq) + 3Ba^2+(aq) => Ba3(PO4)2(s)

#3 is rule 3 above.
F^-(aq) + H^+(aq) ==> HF(aq)

I will leave 2 for you but note CO2.