Why do we balance chemical equations​? Understanding the conservation of mass

Do you know what the connection between burning gas, rusting on iron, and photosynthesis is? We understand that the question is tricky, but the answer is that they are all chemical reactions. A crucial aspect of a chemical reaction is that it must be balanced. But why do we balance chemical equations?

The reason behind it is due to mass conservation. However, as we know you want to thoroughly understand the concept behind this answer, we have prepared this article specifically for you.

So, stay with us, and you will learn the following subjects:

• What is a chemical equation?
• Why do we balance chemical equations?
• How do you balance a chemical equation​?
• Is the chemical equation stoichiometric?
• What happens if chemical equations are not balanced?
• What does stoichiometric mean?
• And much more.

Moreover, if you want to quickly balance a chemical reaction, check out our amazing chemical equation balancer. Let us now show you why it is essential to measure the elements accurately.

In our introduction, we listed different examples of chemical reactions. However, any chemical reaction can be described quantitatively as an equation, which is called a chemical equation.

The simplest way to present a chemical equation is:

where:

• $\mathrm{Reactants}$ — Substances at the beginning of the chemical reaction; and
• $\mathrm{Products}$ — Substances produced at the end of the chemical reaction.

But, if you want to deeply understand your chemical reaction, you need to write explicitly which atoms are your reactants and your products. Besides the proper atoms, you also need to balance your chemical equation, transforming it into a stoichiometric equation. We will show you more explanations about the relevance of balancing chemical equations in the next section.

As previously noted, it is essential to balance a chemical reaction. The fundamental concept behind it is the famous mass conservation. The law of conservation of mass establishes that no matter can be created or destroyed.

In terms of a chemical equation, this means that all matter present in the reactants needs to appear in the products. This is the concept behind stoichiometry, which has a Greek origin meaning "measuring the elements." The correct mass amount also allows us to predict how much product will form and how much reactant we need in a specific chemical reaction.

Let's use an example to show you the difference in writing an unbalanced and a balanced equation for a chemical reaction. Suppose that you want to produce ammonia, so the equation to describe the reaction is:

where:

• $\mathrm{N_2}$ — Nitrogen gas;
• $\mathrm{H_2}$ — Hydrogen gas; and
• $\mathrm{NH_3}$ — Ammonia.

This chemical equation is unbalanced because it has $2$ nitrogen and $2$ hydrogen atoms on the left-hand side and $1$ nitrogen and $3$ hydrogen atoms on the right-hand side.

The chemical reaction that obeys the law of conservation of mass is:

where the multiplicative factors yield us equal numbers of nitrogen and hydrogen atoms on both sides of the equation. These multiplicative factors can be used to compute the molar (or mole) ratios, which represent the ratio of the reactants consumed to the products derived in a chemical reaction. The next step is to understand how you can properly choose the multiplicative coefficients for your chemical equation.

There are specific rules for properly balancing chemical equations. Basically, you need to follow the steps below:

1. Count each type of atom on each side of your equation.
2. Add the correct coefficients to balance the equation.
3. Never change the subscripts inside the formulas.

Some good tips include balancing atoms that appear in only one reactant and one product first, and also computing atom counts after each step.

You can also use a table to balance your equation properly. In the case of the ammonia example, we have:

corresponding to the unbalanced equation:

The table indicates that we are missing one nitrogen atom and have one extra hydrogen atom. To balance the nitrogen, we need to multiply the products by $2$, which results in the following table:

and whose correspondent chemical equation reads:

Now, to properly balance the hydrogen, we need to multiply the second reactant by $3$, obtaining the balanced table:

finally arriving to the stoichiometric equation: