hi, i dont understand how to balance a equation.. plz can u clear it for me??

Balancing a chemical equation is very simple. One has to only make sure that number of elements (and charge in case of redox reactions) on both the sides of the equation are the same.This is in accordance with the law of conservation of mass that the total mass of elements present in the products of a chemical reaction has to be equal to the total mass of elements present in the reactants.

Hence the number of atoms of each element remains the same before and after a chemical reaction.

For example, if we are given the following equation to balance

 H₂SO₄  + S -------> SO₂  + H ₂O (a)

From the above equation, it is quite evident that number of atoms of all the elements are not the same on both the sides of the equation. Hence we will first see the elements whose number of atoms are not the same on both the sides of the equation. 

1) The number of sulphur atoms are unequal. On the left side there are two sulphur atoms, while on the right side there is only one sulphur atom. Therefore we multiply SO₂ in the above equation by 2. The above equation now becomes

 H ₂SO ₄  + S -------> 2SO ₂  + H₂O (b)

2) However, by doing this, the number of oxygen atoms become unequal on both the sides of the equation. There are five oxygen atoms on the right side of the equation and four on the left. In order to balance the number of oxygen atoms, we multiply H₂SO₄  in eqn (b) by 2. The equation now becomes

 2 H ₂SO₄  + S -------> 2SO₂  + H ₂O

3) Now the number of atoms of all the elements are unequal. There are 4 atoms of Hydrogen on the left side of equation and only two on right, 3 atoms of sulphur on left and 2 atoms on right and 8 oxygen atoms on left and 5 on right. If we multiply SO₂ on the right side of the equation by 3 and H₂O by 2, then we find that number of atoms of all the elements on both the sides of the equation become equal. Thus we get

 2 H₂SO₄  + S -------> 3SO₂  + 2H₂O