Question

how can we balance chemical equations?

Answer 1

To balance a chemical equation we just simply need to add number of molecules to the elements on both L.H.S. and R.H.S. so that both the sides of the equation becomes stable.
But we also need to keep in mind that it is an existing equation.Of course no one gives non-existing equations but still you must keep it in your mind.

Answer 2

we need to add number of molecules on the left side of both rhs and lhs to balance the equation.