Question

How to balance chemical equation? Plz explain me

Answer 1

we need to balance the number of atoms of elements on right hand side with the elements on the left hand side.

u will understand better with this example:
H2O----->H2 + 02 
in this equation be need to balance the number of hydrogen atoms and the number of oxygen atoms.

there are 2 atoms of hydrogen and 1 atom of oxygen on the left hand side whereas there are 2 atoms of hydrogen and 2 atoms of oxygen on the right hand side.

we need to add 2 on the left side of H2O on the left hand side and 2 on the heft side of H2 on the right hand side.

these 2s gets multiplied with the number of atoms of the element beside which it lies.

the final equation would look:

2H2O -------------->2H2 + 02

Answer 2

you have to balance a chemical equation by seeing the no.of atoms of each element present on the reactants of the products and reactants side such that no. of atoms of each element have to be equal on both sides.
eg: 2Mg + O2 ----->  MgO
     here there are 2 atoms of Mg and oxygen are there in reactants side where as only one of each in product side so we have to place 2 before MgO to equal the both sides
        2Mg + O2 -------> 2MgO
hence the equation has balanced.