Yield chemistry: Encyclopedia - Yield chemistry

Yield (chemistry)

Yield in chemistry, also known as chemical yield and reaction yield, is the amount of product obtained in a chemical reaction. The absolute yield can be given as the weight in gram or in mol (molar yield). The yield is usually also given as a relative yield, which is the actual yield divided by the theoretical yield (the maximally reachable yield). The relative yield is usually given as a percentage value, the percent yield:

The theoretical yield value always relates to one of the reactants. This is usually the limiting one, taking into account the molar relation of the reactants and the stoichiometry of the reaction.

The maximal 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.

Yield chemistry - 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):

1. 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).
2. Ethanol is used in a 2.5-fold excess (5.0 mol ÷ 2.0 mol).
3. The theoretical molar yield is 2.0 mol (the molar amount of the limiting compound, acetic acid).
4. The molar yield of the product is calculated from its weight (132 g ÷ 88 g/mol = 1.5 mol).
5. The yield is calculated from the actual molar yield and the theoretical molar yield (1.5 mol ÷ 2.0 mol × 100% = 75%).

Category: Physical chemistry

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