Yield is the mass of a product formed during a chemical reaction. It is the ratio of moles of reactants to the moles of products. Yield is the measure of the efficiency of a chemical reaction. In chemistry, there are three different types of yield. i.e, theoretical yield, actual yield, and percentage yield. Yield is usually expressed in the term of percentage yield.
The calculation of yield is a very important parameter for any type of synthesis. It actually measures the efficiency of ongoing procedures. It tells us how many reactants are used and how many products we obtained. Different terms are also used for yield like conversion, selectivity, etc.
Yield is the mass conversion process. It involves the conversion of moles of reactants to moles of products.
Types of yield
Three are three main types of yield
- Actual yield
- Theoretical yield
- Percentage yield
It is the amount of product formed after performing a chemical reaction in the laboratory or through industrial processes. It is also known as experimental yield or true yield. It should always be less than the theoretical yield. Because no reaction is 100% efficient. We cannot recover 100 % of the product through a chemical reaction.
Calculation of actual yield:
Actual Yield is calculated from theoretical and percentage yield. For solid substances, it is calculated in grams.
Theoretical yield = 4g
Percent yield = 72%
By putting values in formula
Actual yield =72 x 4 / 100=2.88g
Factors affecting actual yield
There are different factors that also affect the actual yield i.e, some of the product loss due to filtration because some particles may remain on filter paper. Similarly, some of the products may be lost during rinsing. Some products may dissolve in a solvent. Some products may not fully precipitate out
Similarly there are factors that also decrease our yield i.e reaction conditions, humidity, temperature, light, etc. These factors also may decrease the yield of products. Some reactions require controlled conditions. If these conditions are not achieved then all reactants may not be fully converted into products. This may also affect the yield of the product.
Furthermore, side reactions also decrease actual yield. Similarly, some reactants do not completely react to form products. Some reactions are reversible reactions. So the amount of product form is converted back into reactants. Similarly, impurities in the reactants also affect the actual yield. These factors also lessen the yield of the desired product.
The actual yield will never be more than the theoretical yield. It is against the law of conservation of mass that is
“Total mass of reactants is always equal to the total mass of products”
If the substance is pure then products can not be more than reactants. If the Actual yield is more than the theoretical yield then the product is not pure. There must be some impurities in the product or it may not be fully dried. A small amount of solvent is present in the product.
We can improve our yield of the product by minimizing different types of errors i.e, personal errors and instrumental errors. Similarly, it can be improved by providing proper and controlled conditions required for a chemical reaction.
Theoretical yield is the maximum amount of product that can be made by using stoichiometric calculations. It is calculated from a balanced chemical equation. It involves calculations of molar ratios of reactants to the products. Theoretical yield depends upon limiting reactants. Limiting reactants is present in the smallest amount.
Limiting reactant fully consumed in a chemical reaction. It controls the amount of product formed because it consumes earlier. Theoretical yield tells how much product can be possibly made from a given reactant. Theoretical yield is always greater than actual yield. Because there are different factors that affect actual yield in different ways.
Calculations of theoretical yield
Let’s suppose 3 Kg of CaCO3 is roasted and it produces 1.4 Kg of CaO.
Steps for calculation of theoretical yield
- Write the balanced chemical equation
CaCO3 (s) → CaO (s) + CO2 (g)
- Find out the formula mass of reactant.
Mass of CaCO3= 100g/mol
- Find out the formula mass of the product
Mass of CaO=56 g/mol
- Then calculate the theoretical yield
100 grams of CaCO3 gives 56 grams of CaO
1 gram of CaCO3 gives CaO = 56/100
As 3 Kg= 3000 grams then
3000 gram of CaCO3 gives CaO = 56/100 x 3000 = 1680g
So the theoretical yield is 1680 grams
Whereas actual yield = 1.4 x 1000 = 1400g
Percentage yield = 72%
Actual yield = 2.88g
Theoretical yield =?
By putting values in a given formula
Theoretical yield = 2.88 / 72 x 100= 4.0 g
It is the comparison of actual yield to theoretical yield. Percentage yield tells us how much product finally we have obtained. The yield of products is given in terms of percentage yield. Percentage yield depends upon experimental results as well as stoichiometric calculations.
It is important in the synthesis of any product.
Chemist/ industrialist tries to maximize the percentage yield by improving their process of synthesis. We could not get a 100% yield because of different factors. These factors decrease the actual yield that in turn decreases the percentage yield. If the percentage yield is more than 100% it means our product is not pure.
The efficiency of any chemical reaction depends upon percentage yield. Greater the percentage yield a chemical reaction would be more efficient and vice versa. And a large number of reactants will be converted into products.
Calculation of percentage yield
It is calculated by dividing actual yield by theoretical yield and multiplying the results by 100.
Actual yield = 2.88 gram
Theoretical yield = 4.0 gram
By putting values in the given formula
percentage yield = 2.88 / 4.0 x 100 = 72%
What is meant by yield in chemistry?
In chemistry, yield is the efficiency of chemical reactions. It is the amount of product we obtained from a chemical reaction.
What is meant by theoretical yield?
Theoretical yield is the maximum amount of product that is calculated from a balanced chemical equation. (stoichiometric calculations). It is also knowns as expected yield.
Define actual yield?
The actual yield is the amount of product obtained after performing a chemical reaction.
It is also known as experimental yield.
Why is the actual yield always less than the theoretical yield?
Actual yield is always less than theoretical yield because of
- Incomplete reaction
- Reversible reaction
- Side reactions
- Impurities in reactants
- Improper filtration
- Solubility of products
- Reaction conditions
How theoretical yield is calculated?
Theoretical yield is calculated from a balanced chemical equation. It is calculated by comparing moles of limiting reactant to the mole of the product obtained.
How to balance a chemical equation?
We can balance a chemical equation in three ways
- Ion electron method
- Hit and the trial method
- Redox method
What is meant by limiting reactants?
A limiting reactant is a reactant that controls the amount of product formed during a chemical reaction. Limiting reactant fully consumed. It consumes earlier in a chemical reaction. It is taken in a lesser amount.
Define excess reactant.
The excess reactant is that which is present in excess quantity. It does not fully consume.
It remains after finishing a chemical reaction. It can combine with all of the limiting reactants
How we can calculate percentage yield?
Percentage yield is calculated from theoretical and actual yield. Theoretical yield is calculated from a balanced chemical equation whereas, the actual yield is calculated from the experiment. Then their results are used to find out the percentage yield.
How could we improve the yield of the product?
We can improve the yield of the product by
- Minimizing human errors
- Provide proper conditions for a chemical reaction (controlled conditions)
- Using pure reactants and reagents
- Minimizing the number of steps of chemical reactions
- Using clean and calibrated instruments for a chemical reaction.
- Using dry, washed, rinsed apparatus.
What is if yield actual yield is greater than the theoretical yield?
If the actual yield is greater than the theoretical yield then our product is not pure. Because it is against the law of conservation of mass. It is due to human errors or instrumental errors. Otherwise, the actual yield is always less than the theoretical yield.
What is the importance of yield in chemistry?
Calculation of yield is a very important parameter because
- It quantifies results.
- It tells us the efficiency of the reaction.
- It tells us how much we invest and how much we get back.