How are chemical equations balanced?
Chemical equations are balanced with respect to (i) mass, and (ii) charge.
A fixed mass of reactant, 10, 20, 30 g, gives a fixed mass of product, 10, 20, 30 g. Mass is conserved for every chemical reaction. Charge is also conserved for every reaction. See this old answer.. We can sometimes balance mass and charge systematically and methodically by writing redox reactions .