Answer
$$4 \space NO_2 + O_2 + 2 \space H_2O \longrightarrow 4 \space HNO_3$$
Work Step by Step
1. Identify the chemical compounds:
Nitric acid: $HNO_3$
Nitrogen dioxide: $NO_2$
Oxygen: $O_2$
Water: $H_2O$
2. Write the unbalanced reaction.
$$NO_2 + O_2 + H_2O \longrightarrow HNO_3$$
- Balance the number of hydrogen atoms:
$$NO_2 + O_2 + H_2O \longrightarrow 2 \space HNO_3$$
- Balance the number of nitrogen atoms:
$$2 \space NO_2 + O_2 + H_2O \longrightarrow 2 \space HNO_3$$
- Balance the number of oxygen atoms:
$$2 \space NO_2 + \frac 12 \space O_2 + H_2O \longrightarrow 2 \space HNO_3$$
- Multiply all coefficients by 2:
$$4 \space NO_2 + O_2 + 2 \space H_2O \longrightarrow 4 \space HNO_3$$
