And two or more complete sentences explain how to balance the chemical equation and classify its reaction type. __H3PO4 + __NaBr —> __HBr + ___Na3PO4

 H₃PO₄    +    3NaBr  →    3HBr        +    Na₃PO₄

Explanation:

The unbalanced reaction expression is given as:

            H₃PO₄    +    NaBr  →    HBr        +    Na₃PO₄

We need to balance the expression.

Let us assign variable a, b, c and d and solve mathematically;

       aH₃PO₄    +    bNaBr  →    cHBr        +    dNa₃PO₄

Conserving H : 3a  = c

                   P:   a  = d

                   O :  4a  = 4d

                   Na:   b = 3d

                    Br:    b  = c

Let a  = 1, c  = 3, d  = 1, b  = 3

So:

     H₃PO₄    +    3NaBr  →    3HBr        +    Na₃PO₄

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