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Percentage Yield

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Percent Yield is the ratio of actual yield to the theoretical yield calculated out of 100. The concept of Percent Yield is used in chemistry to calculate the amount of product formed for a given amount of reactant. The actually obtained yield is compared with respect to the theoretically expected yield and expressed in percentage what we call Percentage Yield. The quantity of product received from a chemical process is called the actual yield, whereas the quantity of product produced from the stoichiometric or balanced equation when the limiting reactant is used is called the theoretical yield.

In this article, we will learn in detail about what Percent Yield or Percentage Yield is, the formula to Calculate Percent Yield, and Solved Examples based on it.

What is Percent Yield?

The ratio of actual yield to the theoretical yield when multiplied by 100 is called Percent Yield. It is important in chemistry used to analyze the percentage of conversion of reactant into product. The theoretical yield is calculated using the stoichiometric equation used to represent the chemical reaction. The actual yield is measured in the lab after the reaction has been completed. It should be noted that the units of actual yield and theoretical yield should be the same. The generally preferred units are mole or gram to express actual yield and theoretical yield.

Percentage Yield Definition

Percentage Yield is defined as the ratio of actual yield to the theoretical yield calculated out of 100.

Generally, the value of percentage yield is less than 100 percent since the actual yield produced after the reaction is frequently smaller than the theoretical value. If its value is more significant than 100%, it clearly indicates that more sample was retrieved from the reaction than expected. If the actual and theoretical yields are equal, the percent yield is 100%.

Theoretical Yield

The maximum amount of product that is produced in a chemical reaction is called the Theoretical Yield. Theoretical Yield is the yield of the product based on the theoretical chemical reaction under ideal conditions. In general, the theoretical yield is never achieved in the actual reaction or in the lab due to the presence of impurities and other hindrances from the surrounding.

Percent Yield Formula

Percent Yield Formula is calculated by finding the ratio of Actual Yield and Theoretical Yield and multiplying it by 100 to convert the yield ratio into a percentage. Let’s learn the formula for Percent Yield

P = (A / T) × 100 %

Where,

  • P is the Percentage Yield
  • A is the Actual Yield
  • T is the Theoretical Yield

How is Percent Yield Calculated?

Percent Yield can be calculated using the following steps:

Step 1: First Calculate the Theoretical Yield using a stoichiometric ratio.

Step 2: Measure the actual yield obtained from the experiment

Step 3: Find the ratio of actual yield to the theoretical yield

Step 4: Multiply the ratio by 100 to get the Percentage Yield

The above steps will be easier to understand using examples.

Percentage Yield Examples

Let’s understand the concept of Percent Yield using an example.

Consider the decomposition process of calcium carbonate.

CaCO3 → CaO + CO2

The above reaction indicates that for every mole of reactant, CaCO3, only one mole of the product CaO is obtained. This clearly tells us that the reactant and product have a 1:1 mole ratio.

Suppose for this reaction, we have 2 moles of reactant. This means we will get 2 moles of the product too. But consider that in actuality, the yield was 1.5 moles. To calculate the percentage yield, we find the ratio of actual yield and expected yield.

So, the percentage yield becomes,

P = (1.5/2) × 100 %

⇒ P = 75%

Read More,

Sample Problems on Percent Yield

Problem 1: Calculate the percentage yield of a chemical reaction if 2 moles of the product were obtained against an expected yield of 4 moles.

Solution:

Given,

  • Actual Yield (A) = 2 moles
  • Theoretical Yield (T) = 4 moles

Using the Formula,

P = (A / T) × 100 %

⇒ P = (2/4) × 100 %

⇒ P = (1/2) × 100 %

⇒ P = 50%

Thus, the required Percentage Yield (P) is 50 %

Problem 2: Calculate the percentage yield of a chemical reaction if 5 moles of the product were obtained against an expected yield of 6 moles.

Solution:

Given,

  • Actual Yield (A) = 5 moles
  • Theoretical Yield (T) = 6 moles

Using the Formula,

P = (A / T) × 100 %

⇒ P = (5/6) × 100 %

⇒ P = (0.833) × 100 %

⇒ P = 83.3%

Thus, the required Percentage Yield (P) is 83.3 %

Problem 3: Calculate the actual yield of the product if the percentage yield of a chemical reaction is 90% and the expected yield is 5 moles.

Solution:

Given,

  • Percentage Yield (P) = 90%
  • Theoretical Yield (T) = 5 moles

Using the Formula,

P = (A / T) × 100 %

⇒  A = PT/100

⇒  A = 90 (5)/100

⇒  A = 450/100

⇒  A = 4.5 moles

Thus, the required Actual Yield (A) is 4.5 moles

Problem 4: Calculate the actual yield of the product if the percentage yield of a chemical reaction is 80% and the expected yield is 2 moles.

Solution:

Given,

  • Percentage Yield (P) = 80%
  • Theoretical Yield (T) = 2 moles

Using the Formula,

P = (A / T) × 100 %

⇒  A = PT/100

⇒  A = 80 (2)/100

⇒  A = 160/100

⇒  A = 1.6 moles

Thus, the required Actual Yield (A) is 1.6 moles

Problem 5: Calculate the expected yield of the product if the percentage yield of a chemical reaction is 98% and the actual yield is 3 moles.

Solution:

Given,

  • Percentage Yield (P) = 98%
  • Actual Yield (A) = 3 moles

Using the Formula,

P = (A / T) × 100 %

⇒  T = A/P × 100

⇒  T = (3/98) × 100

⇒  T = 3.06 moles

Thus, the required Theoretical Yield (T) is 3.06 moles.

Problem 6: Calculate the expected yield of the product if the percentage yield of a chemical reaction is 92% and the actual yield is 2.5 moles.

Solution:

Given,

  • Percentage Yield (P) = 92%
  • Actual Yield (A) = 3=2.5 moles

Using the Formula,

P = (A / T) × 100 %

⇒  T = A/P × 100

⇒  T = (2.5/92) × 100

⇒ T = 2.7 moles

Thus, the required Theoretical Yield (T) is 2.7 moles

Problem 7: Calculate the percentage yield for the below decomposition reaction if the number of reactant moles is 6 and the actual yield is 2.8 moles.

2NO → N2 + O2

Solution:

Given reaction indicates that for every 2 moles of reactant, NO, only one mole of the product N2 is obtained. This clearly tells us that the reactant and product have 2:1 mole ratio.

If the number of moles of reactnat is 6, then the product moles are clearly 3. So, the theoretical yield is 3 moles.

Given that the actual product yield is 2.8 moles.

So, the percentage yield becomes,

P = (2.8/3) × 100 %

⇒ P = 93%

FAQs on Percentage Yield

Q1: Define Percent Yield.

Answer:

Percent Yield is the ratio of the actual yield of a reaction to the theoretical yield calculated out of 100.

Q2: How to Calculate Percent Yield?

Answer:

Percent Yield is calculated by dividing the actual yield by theoretical yield and then multiplying it by 100.

Q3: What is Percent Yield Formula?

Answer:

Percent Yield formula is given as follows:

Percent Yield = (Actual Yield/Theoretical Yield)×100

Q4: What is Percent Yield used for?

Answer:

Percent Yield is used for comparison of the actual amount of product formed as compared to the theoretical expectation of product formation.

Q5: Why Percent Yield is Generally not 100?

Answer:

Percent Yield is not 100 because not all reactants get transformed into products as expected theoretically. This is because of incomplete reactions or loss of some reactants during the reaction.



Last Updated : 19 Dec, 2023
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