**Percentage yield**is most often used in chemistry to measure how successful a reaction is; calculating percent yield helps to save resources the next time a synthesis is done as it helps a chemist to understand what is physically possible and what can be expected the next time the synthesis is done.

It also helps chemists find areas that they can modify to cut down on their input while getting the same or even greater output; so here is how you go about calculating percent yield for yourself.

**Instructions to Calculate Percentage Yield**

- First you need to understand what all the terms mean; yield in chemistry is a term that refers to the amount of product that is obtained from a chemical reaction. Actual yield is basically the weight of the actual product in grams or moles, while theoretical yield is the product that was expected to be produced. Fractional or percentage yield is calculated by dividing actual yield by theoretical yield to determine how successful the synthesis actually is when compared to how successful it was expected to be. Once you know the fractional yield, multiply it by 100 to get the percentage yield.
- For example let’s say that actual yield was 50 and expected yield was 150, then the equation would look like this:
- Percentage yield = actual yield/theoretical yield
- Percentage yield = 50/150 = 0.33 fractional yield
- Percentage yield = fractional yield x 100
- Percentage yield = 0.33 x 100 = 33.33%

To calculate percentage yield one must first begin with a balanced equation for the reaction (a balanced equation has the same number of atoms on both sides); next calculate the molecular weight of each reactant and product (add the masses of individual atoms) and then convert all the amounts into moles since you need the amounts in moles before yield calculations can be done. Next you need to figure out the limiting reagent (which reactant will finish first?) with this information you can now calculate the theoretical yield. You would probably already know the actual yield that you got from the synthesis so go ahead and work out the equation.

**TIPS AND WARNINGS**

- If your percentage yield is greater than 100% then do the calculation again and check for errors as the answer should always be less than 100%. If the equation is correct and you still get over 100% then it is probably because the product is impure; purifying the product usually leads to lower yields and more accurate results.
- Although 100% is the ideal result, it is virtually impossible to achieve those results so 90% is considered excellent results and 80% is considered to be very good.
- Ensure that both the theoretical and actual yield figures are in the same units of measurement before you do your calculations.

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