ICSE Class 9 Answered

Balanced chemical equation

When the total number of atoms on the reactant side and the product side is equal, the equation is called a balanced equation.

 

Need for balancing a chemical equation

A chemical equation needs to be balanced because a chemical reaction is just a rearrangement of atoms.

Atoms themselves are neither created nor destroyed during the course of a chemical reaction.

The chemical equation needs to be balanced to follow the law of conservation of mass.

The total mass of the reactants is equal to the total mass of the products. The number of atoms of each element, before the reaction and after the reaction is equal.

 

Steps involved in Balancing a Chemical Equation

Consider the chemical reaction between magnesium and oxygen to understand the steps involved in balancing a chemical equation.

Step 1:

Let us first write the word equation for this reaction.
Magnesium + Oxygen → Magnesium oxide
Step 2

Write the chemical equation for the reaction between magnesium and oxygen.
Mg + O₂ → MgO
Step 3

Count the number of times an element is occurring on both LHS and RHS in this equation.
Mg +  O₂ → MgO

 

Component     Reactant   Product

Magnesium        1              1

Oxygen             2              1
This is an unbalanced equation.

 

Step 4

To balance a chemical equation, first draw boxes around each formula. Do not change anything inside the boxes while balancing the equation.
Choose a reactant or a product that has the maximum number of atoms in it. In that compound, a select the element which has the maximum number of atoms.

In this equation we shall select MgO i.e.magnesium oxide and the element oxygen in it.

To balance the oxygen atoms, let us multiply magnesium oxide molecule by 2 on the right-hand side.The equation can now be expressed as
Component       Reactant    Product 

Magnesium      1 X 2 = 2       2

Oxygen           1 X 2 = 2       2

 

Step 5

There are two oxygen atoms on either side of the equation, but one magnesium atom on the reactants side and two on the product's side. Therefore, multiply the magnesium atom by 2 on the left-hand side.
Component    Reactant     Product

Magnesium     1 X 2 = 2       2

Oxygen              2               2

The balanced equation is

     2Mg +  O₂ → 2MgO
The number of atoms of each element of the reactants = The number of atoms of each element of the products

 

Step 6

Writing Specific conditions on the ArrowThe reaction is carried out in the presence of ‘heat’. On heating, magnesium combines with the oxygen present in the air to form magnesium oxide.

Step 7

Writing symbols of the Physical state to make a chemical equation more informative, the physical states of the reactants and products are mentioned along with their chemical formulae.The gaseous, liquid, aqueous and solid states of the reactants and products are represented by the notations (g), (l), (aq) and (s) respectively.

Using these steps, you can balance any chemical equation.