The above equation represents combustion of methane to produce carbon-dioxide and water.
One carbon atom is present on the reactant side as well as on the product side. Four hydrogen atoms are present on the reactant side and two hydrogen atoms on product side. In order to balance this equation, we would multiply water molecule by two. Now there are four atoms of oxygen in the product side but only two on reactant side, so we will multiply oxygen molecule by two on the reactant side. Now the equation is balanced.
The balanced chemical equation is:
CH4+202-CO2+2H2O
This equation obeys the law of conservation of mass as the mass of the reactants is same as that of the products.
