Verified answer

To balance,

you need to have the same number of atoms on each side.

Let's start with the N_2. This means 2 nitrogen atoms

so, you need to start with

2N H_3 + O_2 ==> N_2 + 3H_2 O

But this still isn't balanced, since we need 3 O's on the lhs

so next try is

2 N H_3 + 3O_2 ==> N_2 + 3H_2 O

We're still not balanced, since we have 6 O's on the lhs and only 3 O's on the rhs

2 N H_3 + 3 O_2 ==> N_2 + 6 H_2 O

and again we check: we need 12 H's on the lhs

so

4NH_3 + 3O_2 ==> 2N_2 + 6 H_2 O

and now the counts are right...

However, I'm not sure that this is a valid reaction (haven't done chemistry in a long time...)

4 NH3 + 6 NO2 = 5 N2 + 12 H2O.

This is the equation for emissions (NOx) control with ammonia injection.

I have not seen ammonia and oxygen reduced to Nitrogen and water.

No. For one thing its not balanced and for another the Pt catalysed oxidation of ammonia gives NO.

4NH3(g) + 5O2(g) --------------> 4NO(g) + 6H2O(g)