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
(HNO3) and nitrogen monoxide (NO). Brown color of nitrogen dioxide gas is disappeared
when reaction occurs.
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
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
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.
Oxides of nitrogen
Lewis structure of nitrogen dioxide
Oxidation nuber of nitrogen dioxide
How to Balance HNO3 = H2O + NO2 + O2 (Nitric acid Decomposing)
In this video we’ll balance the equation HNO3 = H2O + NO2 + O2 and provide the correct coefficients for each compound.
To balance HNO3 = H2O + NO2 + O2 you’ll need to be sure to count all of atoms on each side of the chemical equation.
Once you know how many of each type of atom you can only change the coefficients (the numbers in front of atoms or compounds) to balance the equation for Nitric acid Decomposing.
Important tips for balancing chemical equations:
Only change the numbers in front of compounds (the coefficients).
Never change the numbers after atoms (the subscripts).
The number of each atom on both sides of the equation must be the same for the equation to be balanced.
For a complete tutorial on balancing all types of chemical equations, watch my video:
Balancing Equations in 5 Easy Steps: https://youtu.be/zmdxMlb88Fs
More Practice Balancing: https://youtu.be/Qci7hiBy7EQ
Drawing/writing done in InkScape. Screen capture done with Camtasia Studio 4.0. Done on a Dell Dimension laptop computer with a Wacom digital tablet (Bamboo).