Question

Nitric acid (HNO3) is a component of acid rain that forms when gaseous nitrogen dioxide pollutant reacts with gaseous oxygen and liquid water to form aqueous nitric acid. Write a balanced chemical equation for this reaction. (Note: This is a simplified representation of this reaction.)

Short answer

The balanced chemical equation is \(2 \text{NO}_2 + \text{O}_2 + \text{H}_2\text{O} \rightarrow 2 \text{HNO}_3\).

Step-by-step solution

Write the Unbalanced Equation

Write down the chemical formulas for reactants and products, even if the equation is not balanced yet. The reactants are nitrogen dioxide (\text{NO}_2), oxygen (\text{O}_2), and water (\text{H}_2\text{O}), and the product is nitric acid (\text{HNO}_3). The unbalanced chemical equation looks like this: \[\text{NO}_2 + \text{O}_2 + \text{H}_2\text{O} \rightarrow \text{HNO}_3\]

Balance the Nitrogen Atoms

Begin by balancing the nitrogen atoms. There is one nitrogen atom on each side of the equation, so nitrogen is already balanced.

Balance the Oxygen Atoms

Next, balance the oxygen atoms. There are two oxygen atoms in \text{NO}_2, another two in \text{O}_2, and one in \text{H}_2\text{O}, making a total of five oxygen atoms on the reactant side. In \text{HNO}_3, there are three oxygen atoms. Since the number of oxygen atoms on each side needs to be equal, you will need to write coefficients to balance them. In this case, you can use the coefficient 2 in front of \text{HNO}_3, giving you six oxygen atoms on the product side. Now, you must adjust the reactants to have six oxygen atoms as well. You can do this by adding the coefficient 2 in front of \text{NO}_2 and leaving the \text{O}_2 as it is since it will provide the extra two oxygen atoms needed. The oxygen balance is as follows: \[\text{NO}_2(2) + \text{O}_2(1) + \text{H}_2\text{O}(1) \rightarrow \text{HNO}_3(2)\]

Balance the Hydrogen Atoms

Lastly, balance the hydrogen atoms. There are two hydrogen atoms in \text{H}_2\text{O} and two hydrogen atoms in the two molecules of \text{HNO}_3. The hydrogens are balanced by having one water molecule as a reactant and two nitric acid molecules as products. The balanced chemical equation is as follows: \[2 \text{NO}_2 + \text{O}_2 + \text{H}_2\text{O} \rightarrow 2 \text{HNO}_3\]

Key concepts

Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking of old bonds and the formation of new ones, resulting in the generation of different substances with distinct properties. When balancing chemical equations, it's critical to ensure that the number of atoms for each element is the same on both sides of the reaction. This is known as the law of conservation of mass, stating that matter cannot be created or destroyed in an isolated system. For instance, in the reaction that produces nitric acid, one must account for the atoms of nitrogen, oxygen, and hydrogen to ensure they are balanced.\({
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}To make this concept clearer, let's consider the provided example of nitric acid formation. The initial unbalanced equation is written with the correct formulas for reactants and products. Then, each type of atom was counted and balanced systematically, starting with nitrogen, followed by oxygen, and finally hydrogen. Such an organized approach not only simplifies the process but also ensures no mistakes are made in balancing the equation.

Stoichiometry

Stoichiometry is the section of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It allows chemists to predict the amounts of substances consumed and produced during reactions. In our nitric acid example, stoichiometry would help us understand how much nitrogen dioxide and water are needed to produce a certain amount of nitric acid, and how much oxygen is necessary to fully react with the nitrogen dioxide.\({
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}To dive deeper, the stoichiometry of the balanced equation \[2 \text{NO}_2 + \text{O}_2 + \text{H}_2\text{O} \rightarrow 2 \text{HNO}_3\] reveals that two moles of nitrogen dioxide react with one mole of oxygen and one mole of water to produce two moles of nitric acid. The coefficients in the balanced equation are pivotal; they tell the mole ratio of each reactant and product. This mole ratio is fundamental for calculations involving mass, volume, concentration, and more. Therefore, learning to balance equations correctly is a crucial skill in mastering stoichiometry.

Acid Rain

Acid rain is a serious environmental issue caused primarily by the release of sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere. These substances can originate from natural sources like volcanoes but are primarily emitted by human activities such as burning fossil fuels. Upon entering the atmosphere, these gases react with water vapor to form sulfuric and nitric acids, falling back to the Earth as acid rain.\({
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}The simplified reaction provided for the formation of nitric acid represents just one aspect of the complex chemical processes leading to acid rain. Actual environmental conditions involve numerous chemical interactions and factors such as sunlight, temperature, and pressure. Acid rain can significantly impact ecosystems by acidifying water bodies and soil, leading to harmful effects on plants, aquatic life, and even building materials. Understanding the chemical origins of acid rain helps in developing strategies to reduce the emissions of harmful pollutants and neutralize the acidic compounds before they precipitate.