Question #51215
1 Answer
You can find the steps for balancing redox equations at How do you balance redox equations by oxidation number method?
Your unbalanced equation is
NO₂ + H₂ → NH₃ + H₂O
Step 1. The oxidation numbers are:
Left hand side: N= +4; O = -2; H = 0
Right hand side: N = -3; H = +1; O = -2
Step 2. The changes in oxidation number are:
N: +4 → -3; Change = -7
H: 0 → +1; Change = +1
Step 3. You need 7 atoms of H for every 1 atom of N.
To avoid fractions, we must use 14 atoms of H for every 2 atoms of N. This gives us total changes of +14 and -14.
Step 4. Insert coefficients to get these numbers.
2 NO₂ + 7 H₂ → 2 NH₃ + 4 H₂O
Every substance now has a coefficient. The equation should be balanced,
Step 5. Check that all atoms balance.
Left hand side: 2 N; 4 O; 14 H
Right hand side: 2 N; 14 H; 4 O
The balanced equation is
2NO₂ + 7H₂ → 2NH₃ + 4H₂O
