Write the step-by-step method to balance a chemical reaction.

A balanced chemical equation is one in which the number of atoms of each element on the reactant side is equal to the number of atoms on the product side.

The steps for balancing a chemical equation are:

• Write down the unbalanced equation containing the correct molecular formula of all the reactants and products.
• Determine whether or not the chemical equation is already balanced.
• If the equation is not balanced, start by balancing the elements that occur in the lowest number of reactant and product molecules.
• Balance the remaining elements.
• Make sure that the number of atoms in each element is balanced.

Example:

Let us take the equation: $\mathrm{Fe}+{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{Fe}}_3{\mathrm{O}}_4+{\mathrm{H}}_2$

Step 1: Calculating the number of atoms on both sides of the reaction:

Elements	Number of atoms on the reactant side	Number of atoms on the product side
Fe	1	3
H	2	2
O	1	4

Step 2: Balancing the uneven number of atoms on the reactants and products side:

1. As the number of atoms on the reactants and products side is different, so balancing of iron, hydrogen, and oxygen can be done by multiplying the required coefficient for them in the reaction.
2. This is done by multiplying 3 to iron and 4 to water on the reactant side and 4 to hydrogen on the product side.

$3\mathrm{Fe}+4{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{Fe}}_3{\mathrm{O}}_4+4{\mathrm{H}}_2$

Elements	Number of atoms on the reactant side	Number of atoms on the product side
Fe	3	3
H	8	8
O	4	4

So the balanced chemical equation is:
$3\mathrm{Fe}+4{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{Fe}}_3{\mathrm{O}}_4+4{\mathrm{H}}_2$