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Chemistry is all about dealing with chemical reactions that happen in our surroundings. To understand and study these reactions, we have to write them up in the form of chemical equations.

Before going further in detail about how to study a reaction with these equations or how to balance chemical equations, let us first recall the definition of a chemical equation.

What is a chemical equation?

A chemical equation is a symbolic representation of a reaction mixture to characterize a chemical reaction. An equation comprises three main parts

  • Reactants - The substances which react with each other to form products are called reactants. These are always written on the left-hand side of the arrow.
  • Products - The substances which form as a result of the reaction are called products. These substances are always shown on the right-hand side of the arrow.
  • Arrow - It is a sign which shows the progress of a chemical reaction. It shows the direction in which reaction is proceeding i.e. forward or reverse direction.

Related: How to write chemical equations for an endothermic reaction?

Why does a chemical equation need to be balanced?

Keep in mind that only the balanced chemical equations can help a person to study the entire reaction. If a chemical equation is not balanced,

  1. A person can never predict the type of chemical reaction
  2. A person can never predict the exact quantity and quality of the reaction mixture.
  3. Such unbalanced equations lead to misleading observations and false calculations.

Thus, to get the most exact observations and get the precise readings, you need to learn the ways of balancing complex chemical equations.

As we are using the terms balanced and unbalanced chemical reactions, again and again, the question that arises here is what is the exact meaning of balanced and unbalanced chemical equations?

According to the law of mass conservation, none of the matter can neither be created nor destroyed during a chemical reaction. Thus, a balanced chemical equation is the one in which

"The number of atoms at reactant side is equal to the number of atoms at product side"

To understand it further, let's get help from an example

2H2 + O2 → 2H2O

As it is clear from the equation, there are four hydrogen atoms and two oxygen atoms on the reactant side.

If you look at the product side then there are also four hydrogen atoms and two oxygen atoms. Thus, this equation is a balanced chemical equation and shows which elements, and how many atoms are taking part in the reaction.

The unbalanced chemical reaction is the reverse of it and possesses an unequal number of atoms at both sides as follows

H2 + O2 → H2O

Since there are two hydrogen and two oxygen atoms at the reactant side. while two hydrogens and one oxygen atom at the product side, the equation is not balanced.


  • Always remember that a reaction violating the law of mass conservation is not possible. If the number of atoms is increasing or decreasing at either side.
  • Any equation that does not meet the law of mass conservation is unbalanced.

Fortunately, technology has made it easier for us to balance equations. Today, you can access an efficient online chemical equation balancer.

On finding a balancer, you have to insert the unbalanced equations and wait for a while. Resultantly, the balancer will simplify the equations for you.

Using such technical instruments in examination halls or research institutes is not permitted. Thus, every one of us needs to learn balancing equations even without using such tech tools.

Related: Learn what are redox reactions and how can we calculate redox reactions?

How to balance chemical equations?

Being proficient to balance chemical equations is a pivotal skill in chemistry. So here is a stepwise method for how to balance an equation without using any balance equation calculator.

1. Identify

The very first step is to identify each element taking part in the reaction. Moreover, also find out how many atoms of each element are present in the reaction mixture such as

Fe + O2 → Fe2O3

The reaction mixture consists of two elements i.e. Iron (Fe) and Oxygen (0). There is only one atom of Fe and two atoms of oxygen on the left-hand side.

The equation is unbalanced because the right side has 2 Fe atoms 3 O atoms. So, in this way, identify the element and number of atoms of each element present at both sides.

A Chemical equation calculator can also assist you to find out the exact number of elements participating in the reaction.

2. Add the coefficients

After determining the net number of atoms of one element at the right-hand side of the equation.

Change the coefficients of the same element at the left-hand side to balance atoms at both sides. Let's start with the Fe

Fe + O2 → Fe2O3

By seeing the product side, one can predict that there are two atoms of Fe. So you might think that the equation would work such as

2Fe + O2 → Fe2O3

This might be right for iron but the number of atoms of oxygen is still unbalanced on both sides.

Since the subscript value of oxygen is an even quantity on the left side, to match the subscript value of oxygen on the right side. We have to alter the subscript of iron such as

2Fe2 + O2 → 2Fe2O3

Remember that you are not allowed to change subscripts at the product side since it would change the nature of the product completely.

For example, if we change the subscript value of oxygen on the right side, the product would be Fe2O2. Thus, you have to balance the chemical equation without altering the final product.

3. Balance the other elements

After balancing the number of atoms of one element, repeat the process for the other remaining elements one by one. As we have balanced iron atoms at both sides, let's move towards balancing oxygen atoms.

2Fe2 + O2 → 2Fe2O3

All you have to do is to add a suitable coefficient value for oxygen on the left side. There are six atoms of oxygen on the right-hand side now [2 × O3= six O], so we will balance the equation in this way

2Fe2 + 3O2 → 2Fe2O3

However, it is always better to start with a limiting reactant (a reactant that is present in the minimal amount).

Usually, a limiting reactant can be easily predicted by seeing the equation. Fe is the limiting reactant in this equation since it possesses a lesser number of atoms than oxygen.

Still, to sort out your confusion, you can get help from a limiting reactant calculator.

4. Proofread

In the end, check your equation to make certain that the chemical equation is now balanced completely.

For this purpose, you can use the online equation simplifier, if allowed, or can compare the number of atoms at both sides as follows

2Fe2 + 3O2 → 2Fe2O3
Elements taking part in reaction Total number of atoms at L.H.S Total numbers of atoms at R.H.S
Fe 2 . Fe2 = 4Fe 2 . Fe2 = 4
O 3 . O2 = 6 O 2 . O3 = 6


  • A chemical equation is valid only if it is entirely balanced and shows an equal number of atoms at both sides.
  • Mass can neither be created nor destroyed during a chemical reaction. Instead, it is a constant entity.
  • Add suitable coefficients in the form of simplest whole numbers at both sides to make your equation perfect according to the law of mass conservation.
  • To retain the original identity of reactants and products, you are not allowed to change subscript values.

Sodium react with chlorine to form sodium chloride, learn more about the process and reaction of sodium chloride from here.