Question

Write a balanced equation for the reaction between nitric acid and sodium sulfite.

Short answer

\[ 2 HNO_3 + Na_2SO_3 \rightarrow 2 NaNO_3 + SO_2 + H_2O \]

Step-by-step solution

Write the formulas for reactants

Identify the chemical formulas for nitric acid, which is \( HNO_3 \) and for sodium sulfite, which is \( Na_2SO_3 \).

Write the unbalanced equation

Write down the unbalanced chemical equation with the reactants on the left and the products on the right. Nitric acid reacts with sodium sulfite to produce sodium nitrate (\( NaNO_3 \) and sulfur dioxide (\( SO_2 \)) and water (\( H_2O \)). The unbalanced chemical equation is \( HNO_3 + Na_2SO_3 \rightarrow NaNO_3 + SO_2 + H_2O \).

Balance the sodium atoms

Balance the sodium (\( Na \)) atoms first. There are two sodium atoms in sodium sulfite (\( Na_2SO_3 \) on the reactant side, so we need two formula units of sodium nitrate (\( NaNO_3 \)) on the product side to balance it. The equation now looks like \( HNO_3 + Na_2SO_3 \rightarrow 2 NaNO_3 + SO_2 + H_2O \) .

Balance the sulfur atoms

Ensure that the number of sulfur (\( S \)) atoms is the same on both sides of the equation. As there's one sulfur atom in both the reactant (\( Na_2SO_3 \) and the product (\( SO_2 \)), the sulfur atoms are already balanced.

Balance the oxygen atoms

Balance the oxygen (\( O \)) atoms next. Count the oxygen atoms on both the reactant and product sides. There are 3 from \( HNO_3 \), and 3 from \( Na_2SO_3 \), totaling 6 oxygens on the left. On the right, there are 6 oxygens in two formula units of sodium nitrate (\( 2 \times 3 = 6 \) oxygens) and 2 additional ones in sulfur dioxide (\( SO_2 \)). Since the oxygen atoms are balanced, proceed to the next step.

Balance the hydrogen atoms

Balance the hydrogen (\( H \)) atoms. There is one hydrogen atom from \( HNO_3 \) and two in one molecule of water (\( H_2O \)). So, we need to add another \( HNO_3 \) molecule to make up 2 hydrogens on the reactant side. This changes the equation to \( 2 HNO_3 + Na_2SO_3 \rightarrow 2 NaNO_3 + SO_2 + H_2O \) .

Confirm that all atoms are balanced

Double-check to confirm that the atoms are balanced on both sides. There should be 2 sodium, 2 nitrogen, 7 oxygen, and 2 hydrogen atoms on both sides of the equation.

Key concepts

Chemical Reaction

A chemical reaction is a process where substances, known as reactants, transform into different substances called products. This transformation occurs through the breaking and forming of chemical bonds, leading to a change in the composition and properties of matter.

In the given exercise, nitric acid (\( HNO_3 \) and sodium sulfite (\( Na_2SO_3 \) react to form sodium nitrate (\( NaNO_3 \) sulfur dioxide (\( SO_2 \) and water (\( H_2O \). This is an example of a double displacement reaction, a type of chemical reaction where elements in different compounds exchange places.

When balancing chemical reactions, it's important not only to ensure the number of atoms on each side of the equation is equal but also to understand the underlying process. Knowing the reaction types helps predict the products formed and provides a logical sequence to balance the equation methodically.

Stoichiometry

Stoichiometry is the calculation of the quantities of reactants and products in chemical reactions. It is based on the conservation of mass and the concept of the mole. Stoichiometry requires a balanced chemical equation to ensure that the law of conservation of mass is adhered to.

During the balancing process in our exercise, stoichiometry helps us understand that the coefficients of the reactants and products—the numbers placed before the chemical formulas—correspond to the ratio of moles that react and are produced. For example, the balanced equation shows that 2 moles of nitric acid react with 1 mole of sodium sulfite to produce 2 moles of sodium nitrate, 1 mole of sulfur dioxide, and 1 mole of water. This ratio is crucial when calculating the amount of each substance needed or formed in a reaction.

It's this mole ratio that lets us predict how reactants will combine and what amount of products will form, allowing for precise quantitative analysis in chemistry.

Mole Concept

The mole concept is central to stoichiometry and refers to the unit used to measure the amount of a substance in chemistry. One mole contains exactly 6.022 x 10^23 particles, which could be atoms, molecules, ions, or electrons - a number known as Avogadro's number.

In our balanced chemical equation, the mole concept is implicitly applied. The coefficients show how many moles of each substance are involved. For instance, we can say that 2 moles of nitric acid (\( 2 \times HNO_3 \) will react with 1 mole of sodium sulfite (\( Na_2SO_3 \) to maintain a balanced chemical equation. Understanding the mole concept allows students to determine the mass of reactants needed or the mass of products that can be produced in a chemical reaction, which is a fundamental aspect of chemical calculations.