Class 10 Science

# How to Balance a Chemical Equation

On this page, you will learn how to balance a chemical equation. These notes are based on the chapter Chemical Reactions and Equations from NCERT book based on CBSE syllabus.

• Balancing the equation of reaction involving rusting of iron
• More examples of balancing a chemical equation

Many of you may have found it difficult to balance a chemical equation. Don't worry, you can learn it with practice. This is a step by step guideline to balance a chemical equation.

You will learn to balance the following equation, which shows reaction between iron and moisture in air. This reaction is also called rusting of iron, because rust is formed over iron after this reacction.

Fe + H2O → Fe3O4 + H2

To balance the given or any chemical equation, follow these steps:

Step 1: Write the number of atoms of elements present in reactants and in products in a table, as shown here.

Name of atomNo. on LHSNo. on RHS
Iron13
Hydrogen22
Oxygen14

Step 2: Balance the atom which is the maximum in number, on either side of chemical equation.

In this equation, the number of oxygen atom is the maximum on RHS.

To balance the oxygen one needs to multiply oxygen on LHS by 4, so that number of oxygen atoms becomes equal on both sides.

Fe + 4 × H2O → Fe3O4 + H2

Step 3: Now, the number of hydrogen atoms becomes 8 on LHS, which is more than that on RHS. To balance it, one needs to multiply the hydrogen on RHS by 4.

Fe + 4 × H2O → Fe3O4 + 4 × H2

Step 4: After that number of oxygen and hydrogen atoms becomes equal on both sides. The number of iron is one on LHS, while it is three on RHS. To balance it, multiply the iron on LHS by 3.

3 × Fe + 4 × H2O → Fe3O4 + 4 × H2

Step 5: Now the number of atoms of each element becomes equal on both sides. Thus, this equation becomes a balanced equation.

Name of atomLHSRHS
Iron33
Hydrogen88
Oxygen44

After balancing, the above equation can be written as follows.

3Fe + 4H2O → Fe3O4 + 4H2

## More examples of balancing a chemical equation

### Balance the given equations.

(a) H2 + O2 → H2O

Answer: 2H2 + O2 → 2H2O

Explanation: In this equation, number of hydrogen atoms is 2 on both sides but number of oxygen is 2 on LHS and 1 on RHS. So, as the first step, you need to write 2 before H2O on RHS. After that, number of oxygen atoms becomes 2 on both sides of equation. But number of hydrogen atom becomes 4 on RHS and is 2 on LHS. To balance this, you need to write 2 before H2 on LHS. This makes the equation a balanced one.

(b) Fe + H2O → Fe2O3 + H2

Answer: 2Fe + 3H2O → Fe2O3 + 3H2

Explanation: In this equation, number of Fe atoms is 1 on LHS and 2 on RHS. To balance this, write 2 before Fe on LHS. Now, the equation becomes as follows:

2Fe + H2O → Fe2O3 + H2

Now, number of O is 1 on LHS and 3 on RHS. To balance this, write 3 before H2 on LHS. Now, the equation becomes as follows:

2Fe + 3H2O → Fe2O3 + H2

Now, number of H atoms is 6 on LHS and 2 on RHS. To balance this, write 3 before H2 on RHS. Now, the equation becomes as follows:

2Fe + 3H2O → Fe2O3 + 3H2

Now, number of Fe atoms is 2 on both sides. Number of H atoms is 6 on both sides. Number of O atoms is 3 on both sides. So, this is a balanced chemical equation.

(c) CO2 + H2O → C6H12O6 + O2

Answer: 6CO2 + 6H2O → C6H12O6 + 6O2

Explanation: In this equation, number of C atoms is 1 on LHS and 6 on RHS. To balance this, write 6 before CO2 on LHS. Now, the equation becomes as follows:

6CO2 + H2O → C6H12O6 + O2

In this equation, number of H atom is 2 on LHS and 12 on RHS. To balance this, write 6 before H2O on LHS. Now, the equation becomes as follows:

6CO2 + 6H2O → C6H12O6 + O2

In this equation, number of O atom is 18 on LHS and 8 on RHS. To balance this, write 6 before O2 on RHS. Now, the equation becomes as follows:

6CO2 + 6H2O → C6H12O6 + 6O2

In this equation, number of C atom is 6 on both sides. Number of H atoms is 12 on both sides. Number of O atoms is 18 on both sides. So, this is a balanced chemical equation.

(d) Fe2O3 + C → Fe + CO2

Answer: 2Fe2O3 + 3C → 4Fe + 3CO2

For balancing most of the chemical equations, you can do some guesswork and balance them on the go, as shown in these examples. But when you are a novice, try to make a table and write number of atoms of elements of reactants and products, as shown in the first example. Gradually, you will learn the tricks and can easily balance a given equation.

## Writing the symbols of Physical States of substances in Chemical equation:

By writing the physical states of substances, a chemical equation becomes more informative.

• Gaseous state is represented by symbol g
• Liquid state is represented by symbol l
• Solid state is written by symbol s
• Aqueous solution is written by symbol aq

Writing the condition in which reaction takes place: The condition is generally written above and/or below the arrow of a chemical equation.

Thus, by writing the symbols of physical state of substances and condition under which reaction takes place, a chemical equation can be made more informative.

## Summary

Balanced Equation: Number of atoms of each elements is equal on both sides of equation.

Law of Conservation of Mass: Mass cannot be created and cannot be destroyed.