Question

how to balance chemical equation

Answer 1

It is just try and hit method You just need to do is to count number of each element present in reactants and products and make them equal by increasing molecules of either reactants orproducts

Answer 2

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