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Question Video: Determining the Equation for Calculating the Percentage Yield Chemistry • 10th Grade

What is the formula for calculating the percentage yield from the actual yield and the theoretical yield?

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Video Transcript

What is the formula for calculating the percentage yield from the actual yield and the theoretical yield?

The theoretical yield is the maximum amount of product that can be formed from the given amounts of reactants. For example, if we react 24.3 grams of magnesium with 32 grams of oxygen, we should be able to produce 56.3 grams of magnesium oxide. 56.3 grams is the theoretical yield of this experiment. But when we perform an experiment such as this, it is not possible to produce the theoretical yield.

There are a variety of reasons as to why producing the theoretical yield is not possible. Material may have been lost during experimental procedure, such as transferring a substance from one container to another or during filtration. Other reasons as to why it’s not possible to obtain the theoretical yield include that the reaction may not have completed, unwanted side reactions or competing reactions may have occurred, the reaction may be reversible or in equilibrium, or there may have been impurities in the reactants. Regardless of the reason, the amount of product we produce during an experiment will be less than the theoretical yield. The amount of product actually obtained from carrying out a chemical reaction is the actual yield.

A useful way to express the output or yield of a chemical reaction is as a percentage. We may recall that we can calculate a percentage by dividing the part in question by the total and multiplying by 100 percent. For example, if we wanted to know what percentage of the dots were pink, we would divide four, the number of pink dots, by 10, the total number of dots, then multiply by 100 percent.

We can think of percentage yield in a similar fashion. When thinking about a chemical reaction, the total is represented by the theoretical yield, the maximum amount of product that can be formed from the given amounts of reactants. And the part is represented by the actual yield as when we perform a chemical reaction, we only produce a part of the total amount that we should have been able to make.

So to calculate a percentage yield, we need to take the actual yield and divide it by the theoretical yield, then multiply by 100 percent. So the formula for calculating the percentage yield from the actual yield and the theoretical yield is percentage yield equals actual yield divided by theoretical yield times 100 percent.

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