How Do You Balance Chemical Equations?

Before we answer the question of "how do you balance a chemical equation?" let's take a look at the parts of a chemical equation. When writing a chemical equation, it must clearly indicate what happened, what substances are reacting, what is being created, the total amount, and the conditions under which the substances are in.

1. The reactant and product
   The equation is divided into two distinct halves: the reactants and the products, separated by an arrow.

   Let's take the example of the balanced chemical equation for the combustion of methane to understand the significant parts of a chemical equation.

   $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$

2. Stoichiometric coefficient
   The numbers before chemical formulas denote the stoichiometric coefficient. It represents the ratio of the number of moles of a given substance in the reaction. Also, it's the number that you change when you balance equations to comply with the Law of Conservation of Mass. For example, the 2 in 2O₂ means that the reaction needs two molecules (or two moles) of oxygen molecules. Or CH₄ means that one molecule of methane. A coefficient of 1 is not usually written.

   We would suggest reading our article what is a stoichiometric coefficient, to better understand its significance.

3. Chemical formula subscripts
   To the lower right of the element symbol is a number that indicates the number of atoms of the element in the molecule. Subscripts must never be changed when balancing an equation because changes to the subscripts alter the identity of the substance. For instance, 4 in CH₄ indicates that one molecule of methane contains one carbon atom and four hydrogen atoms. If we were to change this 4 to 3, CH₃ is a methyl group and not methane.

🧪 Three Ways to Balance Chemical Equations

No matter which method you choose, the fundamental goal is always the same: to follow the Law of Conservation of Mass by making sure every atom that starts the reaction finishes it.

1. The Inspection Method (Trial and Error)

Think of this as the standard, go-to approach. It's the simplest, and the one beginners learn first. It's essentially a methodical game of adjusting the coefficients until the atom count for every element is perfectly equal on both sides.

This method is perfect for straightforward and moderately complex reactions, such as when two substances combine (synthesis), when one substance breaks apart (decomposition), or simple swap-out reactions.

2. The Algebraic Method (Solving for X)

If the inspection method feels like hitting a wall, or if the equation is incredibly complex, the algebraic method takes out the guesswork entirely. It's more systematic and mathematical, and it's what computers use to balance equations.

This method is your best bet for those head-scratchingly complex equations that would take forever to solve by trial and error. It's a precise, step-by-step process.

3. The Ion-Electron Method (Half-Reaction Method)

This option is a specialized technique used exclusively for Redox (Reduction-Oxidation) reactions — reactions in which electrons are explicitly transferred from one substance to another. This method cannot be used for simple non-redox reactions.

It is necessary for any reaction where the oxidation states change, particularly when the reaction occurs while the chemicals are dissolved in water (in acidic or basic solutions).

The quickest method would be to use our chemical equation balancer to balance your chemical equation.

Now that we have understood how to balance a chemical equation, let's explore why it is important to balance chemical equations.

• Accurate yields: Every balanced equation gives the exact mole-to-mole ratio. Without it, predicting the volume of the product formed is impossible.

• Industrial scale calculations: Industries like pharmaceuticals, plastics, and fertilizers solely depend on balanced equations to:

  • Use an efficient amount of raw materials;
  • Reduce wastage;
  • Increase product yield; and
  • Incorrect ratios might cost millions.

• Limiting reactants: A balanced equation gives you the knowledge of which of the reactants will run out first, the limiting reactant, which controls the outcome of the reaction.

• Practical safety and accuracy: Unbalanced equations are both unsafe and scientifically inaccurate.

• Safety hazards: Unbalanced equations can lead to:

  • Uncontrolled reactions;
  • Explosions;
  • Toxic or hazardous substances; and
  • Experimental failure.

• An incorrect amount of reactants: can cause:

  • Reactions to stop prematurely;
  • Formation of unwanted byproducts; and
  • Failed experiments.

All of the equations that are to be balanced are subject to a common law,"the law of conservation of mass". This law states that in a reaction, the mass of the product and the mass of the reactant must be the same.

Therefore, the total number of atoms of an element should remain the same on the reactant and product sides, because the atoms that are present are not created or destroyed when the reaction takes place.

So, the two most important steps for balancing chemical equations are:

1. Never change subscripts present in a molecule. Please do not do this, as subscripts are what give each molecule its unique chemical identity. It would also mean that the entire reaction is changed and is chemically infeasible to describe.

2. Only change coefficients when needed. A coefficient does not change the identity of a substance; however, it changes the number of molecules or moles of substance that are present in a reaction. So, it is safe to change the coefficients.