A balanced chemical equation gives us important mathematical relations among the reactants and products. From such mathematical relations we can find the masses of the reactants and products. Consider the following reaction.

2H_{2} + O_{2} ——–→ 2H_{2}0

The chemical equation says 2 moles of hydrogen react with 1 mol of oxygen to yield 2 moles of water. Now 2 moles of H_{2} is 4 g, and 1 mole of O_{2} is 32 g. Therefore, a total of 36 g mass reacts. Similarly, 2 moles of H_{2}O is 2 × (2 + 16) = 2 × 18 = 36 g is the mass of the product. So 36 g of mass of the reactants is consumed to yield exactly 36 g mass of the product. This is in accordance to the law of conservation of mass. Also, it gives us a perception of how much of the mass of individual reactants will be required to produce a certain amount of mass of the product. If the equation was unbalanced, like H_{2} + O_{2} —→ H_{2}O, we wouldn’t have this idea.

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