Percent Yield

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How to Calculate Percent Yield

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Key Questions

  • Answer:

    Percent yield is the ratio of the actual yield to the theoretical yield. (If it is over 100% it means something went wrong.)


    #"Percent yield" = "actual yield" /"theoretical yield"#

    The actual yield is a product that is obtained by experimentation.
    The theoretical yield is obtained through stoichiometric calculation.

    If the two yields are equal, you have 100 % yield.

    Usually you obtain less than 100 %.

    It is impossible to obtain a yield greater than 100%.
    If that happens, some experimental error must have occurred in the creation of the desired product, actual yield.

  • Percent yield represents the ratio between what is experimentally obtained and what is theoretically calculated, multiplied by 100%.

    #"% yield" = ("actual yield")/("theoretical yield") * 100%#

    So, let's say you want to do an experiment in the lab. You want to measure how much water is produced when 12.0 g of glucose (#C_6H_12O_6#) is burned with enough oxygen.

    #C_6H_12O_6 + 6O_2 -> 6CO_2 + 6H_2O#

    Since you have a #1:6# mole ratio between glucose and water, you can determine how much water you would get by

    #12.0# #"g glucose" * ("1 mole glucose")/("180.0 g") * ("6 moles of water")/("1 mole glucose") * ("18.0 g")/("1 mole water") = 7.20g#

    This represents your theoretical yield. If the percent yield is 100%, the actual yield will be equal to the theoretical yield. However, after you do the experiment you discover that only 6.50 g of water were produced.

    Since less than what was calculated was actually produced, it means that the reaction's percent yield must be smaller than 100%. This is confirmed by

    #"% yield" = ("6.50 g")/("7.20 g") * 100% = 90.3%#

    You can backtrack from here and find out how much glucose reacted

    #"65.0 g of water" * ("1 mole")/("18.0 g") * ("1 mole glucose")/("6 moles water") * ("180.0 g")/("1 mole glucose") = 10.8g#

    So not all the glucose reacted, which means that oxygen was not sufficient for the reaction - it acted as a limiting reagent.

    As a conclusion, percent yield problems always have one reactant act as a limiting reagent, thus causing a difference between what is calculated and what is actually obtained. A percent yield that exceeds 100% is never possible, under any circumstances, and means that errors were made in the calculations.

  • The higher the percent yield, the higher the profit for the manufacturer.

    A manufacturer who can get a higher percent yield from a reaction will have more of the product to sell. This will produce more profit for the manufacturer. Industries always strive for high percent yields.


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