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''This is based on the [http://en.wikipedia.org/wiki/Yield_%28chemistry%29 Wikipedia article], accessed October 27, 2006.''

'''Yield''' in [[chemistry]], also known as '''chemical yield''' and '''reaction yield''', is the amount of [[Product (chemistry)|product]] obtained in a [[chemical reaction]]. The '''absolute yield''' can be given as the [[weight]] in [[gram]] or in [[Mole (unit)|mol]] ('''molar yield'''). The yield is usually also given as a '''relative yield''', which is the actual yield divided by the '''theoretical yield''' (the ideal or mathematically calculated yield). The relative yield is usually given as a [[percent]]age value, the '''percent yield''':

:<math>\frac{actual\ yield}{theoretical\ yield} \times 100\ = percent\ yield</math>

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 [[Order (chemistry)|second-order]] reaction of the type A + B &rarr; C):

: 120&nbsp;g '''acetic acid''' (60&nbsp;g/mol, 2.0&nbsp;mol) was reacted with 230&nbsp;g '''ethanol''' (46&nbsp;g/mol, 5.0&nbsp;mol), yielding 132&nbsp;g '''ethyl acetate''' (88&nbsp;g/mol, 1.5&nbsp;mol). The yield was 75%.

# The ''molar amount'' of the reactants is calculated from their weight (acetic acid: 120&nbsp;g  &divide; 60&nbsp;g/mol = 2.0&nbsp;mol; ethanol:  230&nbsp;g &divide; 46&nbsp;g/mol = 5.0&nbsp;mol).
# Ethanol is used in a 2.5-fold excess (5.0&nbsp;mol  &divide; 2.0&nbsp;mol).
# The ''theoretical molar yield'' is 2.0&nbsp;mol (the molar amount of the limiting compound, acetic acid).
# The ''molar yield'' of the product is calculated from its weight (132&nbsp;g &divide; 88&nbsp;g/mol = 1.5&nbsp;mol).
# The ''yield'' is calculated from the actual ''molar yield'' and the ''theoretical molar yield'' (1.5&nbsp;mol &divide; 2.0&nbsp;mol &times; 100% = 75%).

[[Category:Chemistry]]