Balancing Chemical Equations – Steps and Examples

In this article, we’ll learn about balancing chemical equations. Let’s begin with the introduction.

Introduction

In the kitchen, we have seen most of the time that our mother uses a mixture of vinegar and baking soda for various purposes. But then, the question arises, what happens when you mix vinegar and baking soda?

When these two chemicals are mixed, the result is immediate and usually messy. We can easily observe the effervescent cascade of bubbles.

Baking soda and vinegar react chemically as one is a base, and the other is an acid. Baking soda is basic in nature and is called sodium bicarbonate. Vinegar is a diluted solution that contains acetic acid.

The bubbles are of carbon dioxide gas that is produced by the chemical reaction between sodium bicarbonate in the baking soda and acetic acid in the vinegar. The bubbles released when baking soda reacts with an acid play an important role in baking, where the release of gaseous CO₂ causes the dough in your biscuits or the batter in your pancakes to rise.

These types of chemical reactions have been used for thousands of years in baking bread.

Chemical reactions are not limited to cooking; they occur everywhere around us.

For example, We stay alive because of various reactions taking place in our bodies; plants make their food by photosynthesis and the engine of our car runs by the combustion reaction in the internal combustion engine.

In this chapter, we will focus on:

• Chemical reactions.
• Use of chemical formulas to represent reactions.
• Quantitative information about the amounts of substances involved in those reactions.

Stoichiometry

The term Stoichiometry was first discovered by a German chemist named Jeremias Richter. The word “stoichiometry” is derived from the Greek word “stoikhein,” meaning element, and “metron,” meaning measure.

Law of Conservation of Mass

A chemical equation must follow the law of conservation of mass.

The French nobleman and scientist Antoine Lavoisier discovered this important chemical law during the late 1700s.

Lavoisier Stated the Law

“In nature, nothing new is created; an equal quantity of matter exists both before and after the experiment.

Therefore, balancing equations requires the same number of atoms on both sides of a chemical reaction. The number of reactant atoms must be equal to the number of atoms in the product.

For Example

Combustion process: The burning of wood involves the conservation of the mass of wood into oxygen, carbon dioxide, water vapor, and ashes.

Formation of water: To get one molecule of H₂O (water) with a molecular weight of 10, hydrogen with a molecular weight of 2 is added with oxygen, whose molecular weight is 8, thereby conserving the mass.

Chemical Equations

Chemical reactions are represented by chemical equations.

For example,

When the gas hydrogen H₂ burns, it reacts with oxygen O₂ in the air to form water H₂O.

2H₂ + O₂ ⇾ 2H₂O

The substances undergoing chemical changes are called reactants, and their formulas are placed on the left side of the equation. The substances produced by the chemical reaction are called products, and their formulas are placed on the right sight of the equation.

Plus, a sign (+) separates individual reactant and product formulas, and an arrow (⟶) separates the reactant and product (left and right) sides of the equation. The numbers in front of the formulas are the coefficients, which indicate the relative numbers of molecules of each kind involved in the reaction. A coefficient of 1 is typically omitted.

Balancing Chemical Equations

As per the Law of Conservation of Mass, chemical equations must be balanced on both sides, which means matter cannot be created or destroyed. Hence, atoms present on one side of the equation must be present on the other side as well. The number of reactants’ atoms must be equal to the number of atoms in the products. We balance the equation by determining the coefficients that provide equal numbers of each type of atom on both sides of the equation.

For balancing chemical equations, we should know the difference between coefficients and subscripts.

As shown above, the figure changing a subscript in a formula changes the identity of the substance—for example, H₂O and H₂O₂. For example, the chemical H₂O₂, hydrogen peroxide, is completely different from H₂O, i.e., water. Therefore, keep in mind never to change subscripts while balancing an equation. In contrast, when we place a coefficient in front of the formula, it changes only the amount of the substance and not its identity. Thus, 2H₂O means two molecules of water, 3H₂O – three molecules of water, and so on.

A Step-by-Step Solution for Balancing a Chemical Equation

Consider the reaction between one methane molecule (CH₄) and two diatomic oxygen molecules (O₂) to produce one carbon dioxide molecule (CO₂) and two water molecules (H₂O).

CH₄ + O₂ ⟶ CO₂ + H₂O             (unbalanced)

The above equation can be balanced in the following steps:

Step 1:

Write down the correct chemical formulas of reactants and products. Therefore, methane and oxygen are reactants, and carbon dioxide and water are products.

CH₄ + O₂ ⟶ CO₂ + H₂O      (unbalanced equation)

Step 2:

Balance the number of C atoms:

Since 1 carbon atom is in the reactant, one CO₂ molecule is required on the right side.

The coefficients for all these substances must be the same in the balanced equation.

CH₄ + O₂ ⟶ CO₂ + H₂O     (unbalanced equation)

Step 3:

• Balance the number of H atoms.
• On the left, there are 4 hydrogen atoms in the reactants; however, each molecule of water has two hydrogen atoms, so two molecules of water will be required for 4 hydrogen atoms on the right side.
• To balance the H atoms in the equation, we place the coefficient 2 in front of H₂

CH₄ + O₂ ⟶ CO₂ + 2H₂O      (unbalanced equation)

Step 4:

Balance the number of oxygen atoms:

• Here, there are four oxygen atoms on the right-hand side (2 in CO₂ and 2 × 1= 2 in water).
• Therefore, two oxygen molecules are needed to supply the required 4 oxygen atoms.

CH₄ + 2O₂ ⟶ CO₂ + 2H₂O      (balanced equation)

Step 5:

• Confirm that the number of atoms of each element is balanced in the final equation.
• The equation shows 1 carbon atom, 4 hydrogen atoms, and 4 oxygen atoms on each side.

The balanced chemical equation for the combustion of methane:

CH₄ + 2O₂ ⟶ CO₂ + 2H₂O

Indicating the States of Reactants and Products

In chemical equations, generally, the symbols are used to represent the physical states of reactants and products.

We generally use symbols like (g), (l), (s), and (aq) for substances that are gases, liquids, solids, and dissolved in an aqueous (water) solution, respectively.

Thus, the combustion of methane is written as:

CH_4(g) + 2O_2(g) ⟶ CO_2(g) + 2H₂O_(g)

Sometimes, symbols written above or below the reaction arrow indicate the reaction conditions.

For example, The symbol ∆ (Greek uppercase delta), a delta above the reaction arrow, indicates the addition of heat.