Question

Nitric acid 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 the balanced chemical equation for this reaction. (Note: This is a simplified representation of this reaction.)

Short answer

Balanced chemical equation: \( 2 \text{NO}_2(g) + \text{O}_2(g) + \text{H}_2\text{O}(l) \rightarrow 2 \text{HNO}_3(aq) \)

Step-by-step solution

Write the Unbalanced Equation

Start by writing the chemical formulas of the reactants (gaseous nitrogen dioxide (NO2) and oxygen (O2), and liquid water (H2O)) and the products (aqueous nitric acid (HNO3)) without worrying about the stoichiometry. The unbalanced equation is: \[ \text{NO}_2(g) + \text{O}_2(g) + \text{H}_2\text{O}(l) \rightarrow \text{HNO}_3(aq) \]

Balance the Nitrogen Atoms

There is one nitrogen atom on both sides of the equation, so nitrogen is already balanced.

Balance the Oxygen Atoms

Count the number of oxygen atoms on both sides of the equation. There are 2 oxygen atoms in NO2, 2 in O2, and 1 in H2O, making a total of 5 oxygen atoms on the reactants side. On the products side, there is only 1 oxygen atom in HNO3. Therefore, to balance the oxygen atoms, you need to adjust the coefficients. The balanced oxygen gives us this equation: \[ 2 \text{NO}_2(g) + \text{O}_2(g) + \text{H}_2\text{O}(l) \rightarrow 2 \text{HNO}_3(aq) \]

Balance the Hydrogen Atoms

There are 2 hydrogen atoms in H2O on the reactants side and 2 hydrogen atoms in 2 molecules of HNO3 on the products side, so the hydrogen atoms are now balanced.

Verify the Balanced Equation

Confirm that there are now the same number of each type of atom on both sides of the equation. The balanced chemical equation should have 2 nitrogen atoms, 5 oxygen atoms, and 2 hydrogen atoms on both sides: \[ 2 \text{NO}_2(g) + \text{O}_2(g) + \text{H}_2\text{O}(l) \rightarrow 2 \text{HNO}_3(aq) \] This equation is now balanced.

Key concepts

Chemical Reactions

Understanding chemical reactions is fundamental to studying chemistry. A chemical reaction involves the transformation of one set of chemical substances, the reactants, into a new set of substances, the products. When we write a chemical equation, such as the formation of nitric acid from nitrogen dioxide, oxygen, and water, we depict the process of this transformation.

To convey the process with accuracy, the equation must be balanced, meaning that the number of atoms of each element in the reactants must equal the number in the products. This law of conservation of mass is a cornerstone in chemistry. For instance, in the reaction forming nitric acid, we have gases (nitrogen dioxide and oxygen) and a liquid (water) that react to form an aqueous solution of nitric acid. By following the five steps outlined in the solution, we can ensure that the equation is balanced and adheres to this fundamental law.

Acid Rain Chemistry

Acid rain is an environmental phenomenon caused by various chemical compounds in the atmosphere, including the one mentioned in the exercise, which forms nitric acid. Acid rain occurs when emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx), the primary pollutants, react with water vapor and other chemicals in the presence of sunlight to form sulfuric and nitric acids. These acids can fall to Earth as rain, snow, or dry particulate matter, causing harm to ecosystems, buildings, and human health.

The simplified chemical equation provided gives us insight into just a fraction of the complex chemistry behind acid rain. Nitrogen dioxide reacts with oxygen and water to produce nitric acid, shown by the steps to balance the chemical equation. Understanding this process helps us grasp the broader implications of how human activities, such as burning fossil fuels, can lead to changes in natural chemical processes and impact the environment.

Stoichiometry

Stoichiometry is the section of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It allows chemists to predict the amount of product that will form in a reaction based on the quantities of the reactants. This principle is applied when we balance a chemical equation, just as we did for the formation of nitric acid from nitrogen dioxide, oxygen, and water.

Stoichiometry is woven into every step of the solution provided. We begin with an unbalanced equation and then move through successive steps to ensure that the number of atoms for each element is equal on both sides of the equation. This process made use of stoichiometric coefficients, which are the numbers placed in front of the chemical formulas to indicate the proportional amounts of each substance that participate in the reaction. Mastering stoichiometry is critical for anyone looking to work in a chemistry-related field, as it is instrumental in everything from chemical analysis to the development of new products in industries.