| Yield (chemistry) |
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Information About ™Yield (chemistry) |
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: The theoretical yield value always relates to one of the Reactant s. This is usually the limiting one, taking into account the molar relation of the reactants and the Stoichiometry of the reaction. The ideal or theoretical yield of a chemical reaction would be 100%, a value that is rarely reached. Yields above about 90% are called ''very good'', yields above about 75% are called ''good'', yields below about 60% are called ''modest'', yields below about 30% are called ''poor''. Yields can also be above 100% when an extraneous chemical from outside of the reaction has found its way into the yield. EXAMPLE This is an example of an Esterification reaction where one molecule Acetic Acid reacts with one molecule Ethanol , yielding one molecule Ethyl Acetate (a bimolecular Second-order reaction of the type A + B → C): : 120 g acetic acid (60 g/mol, 2.0 mol) was reacted with 230 g '''ethanol''' (46 g/mol, 5.0 mol), yielding 132 g '''ethyl acetate''' (88 g/mol, 1.5 mol). The yield was 75%. # The ''molar amount'' of the reactants is calculated from their weight (acetic acid: 120 g ÷ 60 g/mol = 2.0 mol; ethanol: 230 g ÷ 46 g/mol = 5.0 mol). # Ethanol is used in a 2.5-fold excess (5.0 mol ÷ 2.0 mol). # The ''theoretical molar yield'' is 2.0 mol (the molar amount of the limiting compound, acetic acid). # The ''molar yield'' of the product is calculated from its weight (132 g ÷ 88 g/mol = 1.5 mol). # The ''yield'' is calculated from the actual ''molar yield'' and the ''theoretical molar yield'' (1.5 mol ÷ 2.0 mol × 100% = 75%). |
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