Question

why should we balance a chemical equation?

Answer 1

we need to balance a chemical equation because atom can not be destroyed nor created according to law of conversation of mass

Answer 2

Mass cannot be created nor destroyed according to the law of conservation of mass. Make sure that the number of atoms of a specific element are same on LHS as well as RHS. Writing a number on the side of the comnpund or element means multiplying it by that no. example H2 means 2 atoms of hydrogen but 3H2 means 6 atoms of hydrogen.

Here is an example.
H2 +O2 → H2O
Balanced equation
2H2 + O2 → 2H2O

No. of hydrogen atoms on LHS = No. of hydrogen atoms on RHS = 4
No. of oxygen atoms on LHS = No. of oxygen atoms on RHS = 2
Hence the equation is balanced

I hope it helps.