Question

balance this chemical equation ,

FeS2 + O2 → Fe2O3 + SO2

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 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. ^_^

Answer 2

FeS2 + O2 ---> Fe2O3 + SO2

Now,

In reactant side,

Fe = 1
S = 2
O = 2

In product side,

Fe = 2
S = 1
O = 3+2 = 5

None is balanced

Let us take Fe.

In reactant side 1 and product side 2.

Thus, add 2 before Fe in reactant side.

Now we have,

2 FeS2 + O2 ---> Fe2O3 + SO2

Now, Fe balanced.

In reactant side,

S = 4
O = 2

In product side,

S = 1
O = 5

Now, let us balance S.

We have 4 S in reactant side and 1 S in product side.

Add 4 before S in product side

Now we have the equation,

2 FeS2 + O2 ---> Fe2O3 + 4 SO2

Now, Fe and S are balanced.

Now, let us balance O.

In reactant side we have 2 and in product side we have 11

O is odd in product side. As balancing is hit and trial method let us use one trick. Whenever we get stuck like this, make the odd thing even.

So, add 2 before Fe2O3.

Now,

2 FeS2 + O2 ---> 2 Fe2O3 + SO2

Now, we have 2 Fe in product side and 4 Fe in reactant side. So, add 2 before FeS2.

Thus, 2+2 FeS2 = 4 FeS2

Now,

4 FeS2 + O2 ---> 2 Fe2O3 + 4 SO2

Now, we have 8 S in reactant side and 4 S in product side. Add 4 in reactant side.

4 + 4 SO2 = 8 SO2

Now,

4 FeS2 + O2 ---> 2 Fe2O3 + 8 SO2

We have 2 O in reactant side and 22 O in product side.

So, 22 O = 2 × 11 = 22 O.

Therefore, add 11 before O2.

Now the equation is,

4 FeS2 + 11O2 ---> 2 Fe2O3 + 8 SO2

Now, let us check

In reactant side,

Fe = 4
S = 8
O = 22

In product side,

Fe = 4
S = 8
O = 22

Hence, balanced
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The balanced equation:

4 FeS2 + 11O2 ---> 2 Fe2O3 + 8 SO2