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Balancing of an Unbalanced Chemical Equation in 5 Easy Steps

Chemical Reaction and Equation, Chemistry / By

Balancing of an unbalanced chemical equation means making the number of atoms of various elements equal in reactants and product in an equation.

It is important to note that during balancing a reaction, the formula of a compound (or the subscript of the symbol) must not be changed.
For e.g. –
H2  +  O2  →  H2O
Here,

  • hydrogen has equal number of atoms on both sides but not oxygen. In L.H.S., oxygen has two atoms which is shown by subscript of oxygen (O2 ), but in R.H.S. ,only one atom of oxygen is present in H2O compound.
  • The balancing of equation can not be done by putting subscript ‘2’ on oxygen or in other words, the oxygen atoms can not be balanced by changing formula from H2O to H2O2, it will be a different compound and the chemical reaction will be changed.

The method discussed here for balancing the chemical equation is hit and trial method.
Let us try to balance the following chemical reaction, heated iron metal reacts with steam to form iron (II, III) oxide and hydrogen.
Fe + H2O   →   Fe3O4 + H2

Step -1

Write the chemical reaction in its skeletal equation form (basic form) and underline the each formula.
Fe + H2O   →   Fe3O4 + H2

The significance of underline the each compound is for, nothing should be changed in underlined part or the formula should be kept same. We can only multiply a symbol or a formula by the number like 2, 3, 4…

Step – 2

List the number of atoms of different elements present in reactants and products in the unbalanced chemical equation.

Element       No. of atoms in reactants        No. of atoms in products

Fe                                          1                                                 3

H                                           2                                                2

O                                            1                                                4

Step-3

Start balancing with a compound (either reactant or product) which contains maximum number of atoms. In that compound, select that element which has the maximum number of atoms. Fe3O4 has maximum number of atoms and oxygen is the element which has maximum number of atoms.

To balance oxygen atoms –

No. of Oxygen atoms              Initial                      To balance

In reactants                                    1 (in H2O)                     1 x 4

In products                                    4 (in Fe3O4)                  4 x 1

 

Now the partly balanced equation is –

Fe + 4 H2O   →   Fe3O4 + H2

Step – 4

Balance other elements in similar way to step – 3

To balance hydrogen –

No. of Hydrogen atoms         Initial                            To balance

In reactants                                    4 x 2 = 8 (in 4 H2O )        8 x 1

In products                                     1 x 2 = 2 (in H2)               2 x 4

 

      To balance iron –

No. of Iron atoms                   Initial                     To balance

In reactants                                       1                                   1 x 3

In products                                       3                                   3 x 1

 

      Now, the equation would be –

3 Fe + 4 H2O   →   Fe3O4 + H2

Step – 5

Check the balanced chemical equation again by counting number of atoms of each element on both sides and remove the boxes.

3 Fe + 4 H2O   →   Fe3O4 + H2
Elements            No. of atoms in reactants        No. of atoms in products

Iron                                    3                                                         3

Oxygen                              4                                                         4

Hydrogen                          8                                                        8

Number of atoms of elements in reactants and products are equal. Thus, the equation is now balanced.

These all steps are indicative of sequences. Once all sequences are learnt thoroughly, an equation can be balanced in one step only. A balanced chemical equation means equal numbers of atoms of reactants and products of each type involved in a chemical reaction.   

Similarly, the equation- 3 in balanced form, can be written as –

2 KClO3   →  2KCl + 3O2

 

An chemical equation can be made more informative by adding –

(a)  Symbols of physical state

The physical states of the reactants and products are mentioned by putting state symbols (‘g’ for gaseous; ‘l’ for liquid; ‘aq’ for aqueous and ‘s’ for solid) alongwith their chemical formulae.

3Fe (s) + 4H2O (g)      →     Fe3O4 (s) + 4H2 (g)

The above chemical equation is clearly indicating that Fe and Fe3O4 are solids whereas H2O and H2 are gaseous in nature. The word aqueous (aq) is written where the reactant or product is present as a solution in water.

In general, physical states do not include in a chemical equation unless it is necessary to specify them.

(b)  Other conditions such as temperature, pressure, catalyst etc.

Exothermic or endothermic nature of a chemical reaction can be shown as

N2 (g) + O2 (g) + Heat → 2 NO(g)                                (Endothermic reaction)

C (s)  + O2 (g)   → CO2(g) + Heat                                 (Exothermic reaction)

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + Heat         (Exothermic reaction)

2 Mg (s) + O2 (g) → 2 MgO(s) + Heat                        (Exothermic reaction)

The other special conditions for a chemical reaction such as specified temperature or a temperature range, pressure, catalyst etc. are shown above and / or below the arrow in the equation. For e.g.,

 

  1. w Fe + x H2O → y Fe3O4 + z H2
    When the equation is balanced, the coefficient w, x, y, z respectively are –
    Submit the answer

 

Next –

Types of Chemical Reaction – Combination Reaction