# Percent Yield

## Key Questions

• 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 (${C}_{6} {H}_{12} {O}_{6}$) is burned with enough oxygen.

${C}_{6} {H}_{12} {O}_{6} + 6 {O}_{2} \to 6 C {O}_{2} + 6 {H}_{2} O$

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.

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

#### Explanation:

$\text{Percent yield" = "actual yield" /"theoretical yield}$

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.