Balance Equation - Class 7 PDF Download

What is a chemical reaction?

Chemical reactions are everywhere, from how we exchange oxygen and carbon dioxide to rays of light falling on us from the sun, they all involve chemical reactions. A chemical reaction can be described as a transformation reaction wherein one chemical entity undergoes a change in parameters, could be atomic structure or a physical change like evolution of heat.

Representing a chemical reaction

In a chemical reaction the entities to the left of the arrow are called the reactants and the entities formed on the right side once the reaction occurs are called the products.

A + B → C + D

(Reactants) (Products)

A chemical reaction is a basic representation of what all react together to form the products.

Why do we balance chemical reactions?

So as to be in accordance with the law of conservation of mass, we balance chemical reactions. This helps us to determine the required quantity of reactant or product such that the reaction is feasible with minimal wastage of resources.

Balancing involves making sure that the number of atoms of a particular element are the same on the left side of the reaction and the right side of the reaction. But it’s just not that easy as there a lot more factors to look into while balancing chemical reactions. Let us look at the steps involved to balance chemical reactions.

How to balance a chemical reaction?

Step 1: Write down the chemical reaction

• Once you know the chemical reaction which you have to balance, write down the unbalanced basic chemical reaction.
• Usually the chemical reaction will be given.
• If not, from your understanding of the nomenclature of compounds, figure out the chemical formula of the reactants and products and arrange them on the respective sides of the chemical reaction.

Step 2: Calculate the number of atoms

• Once you have the basic unbalanced chemical reaction, count the number of atoms of a particular element on the reactant side as well as the product side.
• On the basis of the law of conservation of mass, mass is neither created nor destroyed in a chemical reaction.
• Now we comparing the number of atoms on for a particular element on both sides of the arrow.
• If they are the same, the equation is already balanced.
• If they are not the same, the equation is balanced and we need to balance the chemical reaction.

Step 3: Adding coefficients to the molecules to balance the chemical reaction

• To balance the chemical reaction, we add coefficients to the molecules rather than to the individual element’s atoms. As adding atoms to the molecules would change the nature of the molecule. Thus we change the number of molecules that are a part of the reaction to balance the chemical reaction.
• The first step involved would be to balance out a single molecule of reactant & product first.
• Keep the task of balancing hydrogen and oxygen for last as usually once you are done with the rest, hydrogen and oxygen should be already balanced. Also, oxygen and hydrogen will be fused with other compounds usually, thus trying to balance them first will make the process much more complex.
• This strategy is called as balancing by inspection.

Step 4: Balance the required amount of Oxygen & Hydrogen 

• Once the rest of the reactants are balanced, find the right ratio of oxygen or hydrogen atoms such that the numbers will be equal on both sides of the arrow.

Thus you have learned the theory behind how to balance a chemical reaction. Let us get into a bit more detail and practice with the help of an example.

Example:

Consider the case of rusting of Iron.

Step 1:

We identify the reactants and products. In the case of rusting of iron, we have Iron and oxygen reacting to give iron oxide.

Which can be represented as :

Fe+O2→Fe2O3

Iron reacting with oxygen to provide iron oxide, the chemical name of rust.

Step 2:

Number of atoms in reactant side:

• Fe : 1
• O : 2

Number of atoms in product side:

• Fe : 2
• O : 3

Step 3:

To balance the number of Fe atoms we compare the reactant and product sides.

We can balance it by giving the iron on the reactant side a coefficient of 2.

2Fe+O2/→Fe2O3

But if we consider the case of oxygen as well we can see that we will again have to multiply the reaction by a larger number to make the equation balanced. Thus we give a coefficient of 4 on the reactant side.

4Fe+O2→2Fe2O3

Step 4:

Now to balance the number of oxygen atoms. Counting the number of atoms, we can see that the equation can be balanced by having 3 molecules of oxygen each with 2 atoms on the reactant side.

4Fe+3O2→2Fe2O3
Thus, we have the balanced equation stating the rusting of iron.