Question

what are rules of balancing a chemical equation?

Answer 1

What is a Balanced chemical equation? 
An equation having same mass on both sides of the equation is called Balanced chemical equation. 

Why do we balance the chemical equation? 
We balance the chemical equation because the total mass of the elements present in the products of a chemical reaction same as the total mass of elements present in reactant. 
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Let's take an example:-
 
Let's balance ----- FeS2 + O2 ⇒ Fe2O3 + SO2 
To balance an equation first we need to count the number of atoms of different elements present in the unbalanced equation. 

We should start balancing with the compound which is odd. 

In Fe2O3, 3 is odd.  

Write 2 before Fe2O3. 

Now our partly balanced equation is =  FeS2 + O2 ⇒ 2Fe2O3 + SO2 

NOTE:- When we balance, We can only write numbers before compound!

Now, there are 4 atoms of Fe on the right side of the equation. Therefore, We will write 4 before FeS2 to balance Fe.

Now, our equation is =  4FeS2 + O2 ⇒ 2Fe2O3 + SO2 

Now, there are 8 atoms of S on the left side of the equation. Therefore, We will write 8 before SO2 to balance S.

Now, our equation is =  4FeS2 + O2 ⇒ 2Fe2O3 + 8SO2 

Now, there are 22 atoms of O on the right side of the equation and only 2 on the left side. Therefore, We will write 11 before O2 to balance O.

Now our balanced equation is =  4FeS2 + 11O2 ⇒ 2Fe2O3 + 8SO2 

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Let's check whether our equation is balanced or not.

There are 4 atoms of Fe on both sides of the equation.
There are 8 atoms of S on both sides of the equation.
There are 22 atoms of O on both sides of the equation.

Hence, The equation is balanced. ^_^

By this way u can balance an equation. Steps and rules are mentioned above!