Difference between Percent Yield and Theoretical Yield | Hacker Noon

June 25th 2020

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@james-johnsonJames Johnson

I am a researcher and a technical content writer. A math teacher since 2007. I love travelling, Love

When it comes to knowing about the amount of resultant product of a chemical reaction, one thing which is a must to do is yield calculations.

Yield in chemistry is known as the total amount of product as a result of a chemical reaction. Yield is also referred to as reaction yield or absolute yield. The absolute yield is weighed in terms of grams (g) and moles (mol).

Types of Yield

Absolute yield has three types to obtain the products of a chemical reaction. Each type made up different values accordingly, the requirements.

Theoretical Yield

It is the maximum amount of the product obtained from a chemical reaction, it is known as theoretical yield and it is not a laboratory depending calculation.

Actual Yield 

It is the total amount of products of a chemical reaction achieved in the laboratory, not alike theoretical yield.

Percent Yield

It is the percentage ratio of the total amount of products taken by a chemical reaction.

    %Yield = Actual Yield/ Theoretical Yield x 100

Difference between Theoretical Yield and Percent Yield

Both the calculations are different in their own uniqueness of calculating method; the exact same goes for the answers each yield obtains.

When it comes to calculating the maximum amount of products from the given limiting reactants of a balanced chemical reaction, we call it a theoretical yield. While if you need to know the percentage of the total product, you must know the ratio of both theoretical yield as well the actual yield of the total amount of product of a chemical reaction to determine the percentage ratio.

The final answers for both yield calculations are completely different from each other even if the amount of products and the given reactants are the same.

Theoretical yield can range in between from 0 to 100, but percentage yield can vary in ranges.

To give you an elaborate view on theoretical and percent yield, here are the calculation methods of  both below.

How to calculate Theoretical yield?

To calculate the theoretical yield of any reaction, you must know the reaction. Let’s look at the following reaction where at heating potassium chlorate (KClO3), it produces oxygen gas (O2).

2 KClO3 (s) → 3 O2 (g) + 2 KCl (s)

The balanced equation reaction shows that 2 moles of KClO3 will produce 3 moles of O2 and 2 moles of KCl. To calculate the theoretical yield, use these ratios as a conversion factor. Here is a typical example problem.

Step 1: 

We need to know the amount of KClO3 in moles to use the conversion, so the first step is to convert grams KClO3 to moles KClO3. To make it easier, know the molecular mass of KClO3 is 122.55 g/mol.

6 = x moles KClO3

Step 2: 

Use the chemical equation to relate moles KClO3 to moles O2.

x moles O2 = 3 x 3 moles O2

 x moles O2 = 9 moles O2

6 moles of KClO3 (735.3 grams of KClO3) will produce 9 moles of O2 gas.

How to calculate Percent Yield?

To determine the percentage ratio of the product of the chemical reaction, you need to follow the above method to calculate theoretical yield and also need to know the actual yield, which is obtained at the labs. 

For %yield you have the formula 

%yield = Actual yield/ Theoretical Yield x 100

What you need to do is to divide the ratios of both actual and theoretical yield and then multiply the answer with 100 to get the percentage.

Let’s suppose we have the following ratio for each yield.

We have the actual yield for sodium sulfate is only 37.91g, and according to the theory, sodium sulfate has a theoretical yield of 46.59g. So the percentage yield would be something like

%Yield = 37.91g/46.59g x 100 =81.37% 

You got your answer, i.e 81.37% yield.

There are online calculators like theoretical yield calculator and percent yield calculator which anyone can find easily. Online calculators are usually accurate and provide correct results. All those who have not mastered calculating theoretical yield & percent yield manually, must use online calculators so that they could practice & learn at the same time.
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