Nitrogen Dioxide and Water Reaction | NO2 + H2O

Nitrogen dioxide (NO2) is an acidic gas and readily reacts with water (H2O) to produce an acidic solution of nitric acid (HNO3) and nitrogen monoxide (NO). Brown color of nitrogen dioxide gas is disappeared when reaction occurs.

nitrogen dioxide + h2o reaction

Nitrogen dioxide gas reacts with water to produce nitric acid and nitrogen monoxide.

This reaction happens very easily in water. Therefore, produced nitrogen dioxide gas is sent to water to manufacture nitric acid in chemical industry. This reaction is a redox reaction.

NO2 + H2O → HNO3 + NO

Sometimes, we write the chemical equation of nitrogen dioxide and water as below.

2NO2 + H2O → HNO3 + HNO2

In this reaction (consider as reaction 1), we see nitric acid and nitrous acid are formed as products.

Why there are two equations to express products of nitrogen dioxide and water reaction? We can explain it like this.

  • Nitrous acid is an unstable acid and readily decomposes to nitric acid, water and nitric oxide.
  • HNO2 → HNO3 + NO + H2O

When we balance this equation (consider as reaction 2),

  • 3HNO2 → HNO3 + 2NO + H2O

By combining reaction 1 and reaction 2 to remove nitrous acid from major equation, we will get our proper equation. ( 3 * reaction 1 + reaction 2 )

  • 6NO2 + 3H2O + 3HNO2 → 3HNO3 + 3HNO2 + HNO3 + 2NO + H2O
  • 6NO2 + 2H2O + → 4HNO3 + 2NO
  • 3NO2 + H2O + → 2HNO3 + NO

  • NO2 is a brown color gas. It's brown color is disappeared when NO2 reacts with water.
  • This reaction is industrially used for nitric acid production from ostwald method.
  • Also, this is the reaction which causes acid rains from nitrogen dioxide gas in the atmosphere.
  • This reaction is a disproportionation reaction because nitrogen on nitrogen dioxide molecule is reduced and oxidized. This is discussed in detail later on this tutorial.
  • Due to reaction with water, nitrogen dioxide dissolve very well in water.

Balanced chemical equation with physical states

Gaseous nitrogen dioxide reacts with liquid water and produce nitric acid which is highly soluble in water (therefore, nitric acid exists as an aqueous solution) and gaseous nitrogen monoxide.

3NO2(g) + H2O(l) → 2HNO3(aq) + NO(g)

NO2 + H2O is a disproportionation reaction

Oxidation number of nitrogen at NO2 is +4 according to the lewis structure of NO2. When reaction occurs, NO2 is oxidized to nitric acid. In nitric acid, oxidation number of nitrogen is +5. Simultaneously to the oxidation, another NO2 molecules are reduced to NO. The oxidation number of nitrogen in NO is +2. Therefore, nitrogen atom in NO2 is reduced and oxidized simultaneously and those reactions are defined as disproportionation reactions.

Uses of nitrogen dioxide and water reaction

This reaction is used in nitric acid production; ostwald process. Produced nitrogen dioxide gas is sent to water to produce nitric acid. As a by product, nitric oxide (NO) is produced. It is also used to produce nitric acid by separating and converting to nitrogen dioxide in the manufacturing process.

Nitrogen dioxide and water balanced equation

3NO2(g) + H2O(l) → 2HNO3(aq) + NO(g)

Questions asked by students

Ask your question and find the answer free.

Oxidation number of nitrogen in nitrogen dioxide is +4. Also oxidation number of nitrogen in dinitrogen trioxide is four. Will both nitrogen dioxide and dinitrogen trioxide will react with water in same way?

As nitrogen dioxide, dinitrogen trioxide reacts with water and form nitric acid and nitric oxide. Therfeore oxidation number of nitrogen is changed when both nirogen dioxide and dinitrogen trioxide react with water.

What is the pH value when nitrogen dioxide dissolve in water? (when nitrogen dioxide reacts with water)

pH value will be lover than seven because of nitric acid formation. If lot of nitrogen dioxide is dissolves, pH value will be a value like 1,2 forming a strong acidic solution (Nitric acid is a strong acid).

How do I use NO2 + H2O reaction to test NO2 gas and Br2 gas?

Both bromine and nitrogen dioxide gases are brown color gases. Therefore we cannot identify them, by observing their colors.

In this tutorial, we have learned that NO2 will readily reacts with water and lost it's brown color during the reaction. But, bromine gas which is a brown color too, does not dissolve like NO2. So brown color of Br2 remains in the water.

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