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Question 3: Explain why balanced chemical equations are used in stoichiometric problems?


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.

2H2 + O2 ——–→  2H20

The chemical equation says 2 moles of hydrogen react with 1 mol of oxygen to yield 2 moles of water. Now 2 moles of H2 is 4 g, and 1 mole of O2 is 32 g. Therefore, a total of 36 g mass reacts. Similarly, 2 moles of H2O 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 H2 + O2 —→ H2O, we wouldn’t have this idea.


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