The theoretical yield of a chemical reaction is the maximum amount of product that can be obtained when the limiting reactant is completely consumed. Calculating the theoretical yield involves determining the mole ratio of each reactant, finding the limiting reactant, and multiplying the ratio of moles of product to moles of limiting reactant by the moles of available limiting reactant. Inorganic reactions often produce close to 100% of the theoretical yield, while organic reactions in industry rarely do. Calculating the theoretical yield in real-world environments can be challenging due to factors such as corrosion and impurities.
The theoretical yield of a chemical reaction is the obtained amount of a product of a reaction in which the limiting reactant has been completely consumed. As chemists learn to balance chemical equations, in practice a reactant will be present in amounts less than stoichiometric. The reactant will limit the amount of product possible from the reaction. The method for calculating the theoretical yield is simple. Applying this calculation in a real-world environment is more useful, but more complex.
In the first step of calculating the theoretical yield, the balanced chemical equation is written and the mole ratio of each reactant is examined. The amount of each reactant is determined by weighing the reactants, measuring concentrations, or using standard solutions. The limiting reactant is found by converting the amount of reactants present into moles of each reactant and determining, based on the ratios from the first step, which reactant will be used up before all other reactants are used. The ratio of moles of product to moles of limiting reactant from the balanced equation is multiplied by moles of available limiting reactant to find moles of product. Then using the molecular weight of the product, this response is converted to grams of product or other suitable measure.
In the laboratory, chemists start with a proposed reaction. The reaction products are predicted and confirmed experimentally. A balanced chemical equation is written using knowledge of the reaction. Given the starting concentrations of each reactant, the limiting reactant is chosen and the yield is calculated based on whether that reactant is completely converted to product. In future experiments or sample analyses, the actual yield will be compared with the theoretical yield and the causes of product loss determined.
To calculate the theoretical yield it is necessary to know the reactants and products of the reaction. This can be more challenging in real industrial environments than laboratory conditions. The reaction, for example, could take place in an acidic or basic condition, and there could be corrosion of the pipes releasing metals that could act as catalysts. Laboratory calculations should be supported by samples from the process of interest.
Typically, inorganic reactions, particularly those that produce a solid precipitate or volatile product, can be conducted under conditions that result in a complete reaction of the limiting reactant. These reactions can often produce close to 100% of the theoretical. Organic reactions often produce many more byproducts due to less pure reactant streams and the multiplicity of possible reactions. Industrial processes involving organic reactions in industry rarely produce results approaching the theoretical yield. These processes usually require subsequent separation and purification steps.
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