En química, el rendimiento, también referido como rendimiento químico y rendimiento de reacción, es la cantidad de producto obtenido en una reacción química. El rendimiento absoluto puede ser dado como la masa en gramos o en moles (rendimiento molar). El rendimiento fraccional o rendimiento relativo o rendimiento porcentual, que sirve para medir la efectividad de un procedimiento de síntesis, es calculado al dividir la cantidad de producto obtenido en moles por el rendimiento teórico en moles: Para obtener el rendimiento porcentual, multiplíquese el rendimiento fraccional por 100% (por ejemplo, 0,673 = 67,3%). Uno o más reactivos en una reacción química suelen ser usados en exceso. El rendimiento teórico es calculado basado en la cantidad molar del reactivo limitante, tomando en cuenta la estequiometría de la reacción. Para el cálculo, se suele asumir que hay una sola reacción involucrada. El rendimiento teórico o ideal de una reacción química debería ser el 100%, un valor que es imposible alcanzar en la mayoría de puestas experimentales. De acuerdo con Vogel, los rendimientos cercanos al 100% son denominados cuantitativos, los rendimientos sobre el 90% son denominados excelentes, los rendimientos sobre el 80% muy buenos, sobre el 70% son buenos, alrededor del 50% son regulares, y debajo del 40% son pobres. Los rendimientos parecen ser superiores al 100% cuando los productos son impuros. Los pasos de purificación siempre disminuyen el rendimiento, y los rendimientos reportados usualmente se refieren al rendimiento del producto final purificado.

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In chemistry, yield, also referred to as reaction yield, is the amount of product obtained in a chemical reaction. The absolute yield can be given as the weight in grams or in moles (molar yield). The percentage yield (or fractional yield or relative yield), which serves to measure the effectiveness of a synthetic procedure, is calculated by dividing the amount of the desired product obtained by the theoretical yield (the unit of measure for both must be the same): The theoretical yield is the amount predicted by a stoichiometric calculation based on the number of moles of all reactants present. This calculation assumes that only one reaction occurs and that the limiting reactant reacts completely. However the actual yield is very often smaller (the percent yield is less than 100%) for several reasons: \n* Many reactions are incomplete and the reactants are not completely converted to products. If a reverse reaction occurs, the final state contains both reactants and products in a state of chemical equilibrium. \n* Two or more reactions may occur simultaneously, so that some reactant is converted to undesired by-products. \n* Losses occur in the separation and purification of the desired product from the reaction mixture. \n* Impurities are present which do not react The ideal or theoretical yield of a chemical reaction would be 100%. According to Vogel's Textbook of Practical Organic Chemistry, yields around 100% are called quantitative, yields above 90% are called excellent, yields above 80% are very good, yields above 70% are good, yields above 50% are fair, and yields below 40% are called poor. These names are arbitrary and not universally accepted, and for many reactions these expectations may be unrealistically high. Yields may appear to be above 100% when products are impure, as the measured weight of the product will include the weight of any impurities. Purification steps always lower the yield and the reported yields usually refer to the yield of the final purified product. When more than one reactant participates in a reaction, the yield is usually calculated based on the amount of the limiting reactant, whose amount is less than stoichiometrically equivalent (or just equivalent) to the amounts of all other reactants present. Other reagents present in amounts greater than required to react with all the limiting reagent present are considered excess. As a result, the yield should not be automatically taken as a measure for reaction efficiency.

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