# 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