The reaction of phosphoric acid (H₃PO₄) with trisodium phosphate (Na₃PO₄) is a neutralization reaction that produces disodium hydrogen phosphate (Na₂HPO₄) and sodium dihydrogen phosphate (NaH₂PO₄).

Here's the balanced chemical equation:

H₃PO₄(aq) + 2Na₃PO₄(aq) → 3Na₂HPO₄(aq) + NaH₂PO₄(aq)

Explanation:

* Phosphoric acid (H₃PO₄) is a triprotic acid, meaning it can donate three protons (H+).

* Trisodium phosphate (Na₃PO₄) is a strong base.

* The reaction involves the transfer of protons from the acid to the base.

The reaction can be explained in steps:

1. First proton transfer: H₃PO₄ reacts with Na₃PO₄ to form Na₂HPO₄ and NaH₂PO₄.

2. Second proton transfer: H₃PO₄ reacts with another molecule of Na₃PO₄ to form another molecule of Na₂HPO₄.

3. Third proton transfer: The remaining H₃PO₄ reacts with the last molecule of Na₃PO₄ to form another molecule of Na₂HPO₄ and a molecule of NaH₂PO₄.

Overall, the reaction results in the formation of disodium hydrogen phosphate (Na₂HPO₄) and sodium dihydrogen phosphate (NaH₂PO₄) in a 3:1 molar ratio.

Note: This reaction is highly dependent on the stoichiometry of the reactants. If there is an excess of phosphoric acid, the final products will be different.