Introduction to the percent yield
A chemical reaction consists of two main entities; reactants and products. Yield is the quantity of the total amount of product synthesized due to a chemical reaction in relation to the quantity of consumed reacting mixture. A chemical reaction has many chemical factors or conversion factors depending upon its nature. It is always represented in percentage.
In chemistry, we deal with three different types of yield as follows.
- Theoretical yield - It is the total amount of product predicted from the balanced equation of the corresponding chemical reaction. For example, you predict that you will score 80% in your next chemistry exam, then this 80% is your theoretical yield of effort.
- Actual yield - It is the total amount of product that is actually obtained after the reaction. For example, you thought about scoring 80% in an exam but got 78%, then it is your actual yield.
Since some mass gets converted to energy during the reaction, the actual yield is always lesser than the theoretical one.
- Percent yield - It is the ratio of theoretical yield to the actual yield. If a chemical reaction gives a similar actual and theoretical yield, its percent yield will always be 100%.
How to Calculate Percent Yield Step by Step?
Step 1: Understand the requirements
As stated before, the theoretical yield is always higher than that of the actual yield. The reason is the failure of some reactants to change into products due to various factors like unforeseen problems, the presence of contaminants, and mass-energy conversion. The percent yield definition tells the ratio of both these types of yield, and to calculate it; we use the given percent yield formula which is also known as percent yield equation.
Percent yield = Theoretical yield ÷ Actual yield × 100
Thus there is no worry about how to find percent yield, to get the value of percent yield, you need to find out the values for theoretical and actual yield first and just putting in in the percent yield formula. If the percent yield of a reaction is 60%, then it means that you got the actual yield equal to 60% of your theoretical yield.
Related: Find what is synthesis reactions in chemistry with examples.
Step 2: Calculate the Actual Yield
If you performed the reaction by yourself, then there will be no problem at all in calculating the actual yield. You have to weigh your product using a balance and note the value of the total product mass.
You can also balance your equations using online chemical equation balancer on the home page of this website.
Step 3: Calculate the Theoretical Yield
There are two main methods to find the theoretical yield of a reaction. The one used to find theoretical yield at the industrial level and the other that is used to calculate theoretical yield at more minor levels (for few moles)
For this purpose, all you have to do is to multiply the number of moles with the molar mass of each reactant and then sum up all the values together, such as
2H2 + O2 - - - > 2H2O
2(2) + 2(16) = 36g
Thus, the theoretical yield of water produced by the reaction of two moles of hydrogen and one mole of oxygen will be 36g.
CO + 2H2 - - - > CH3OH
Suppose you have been asked to find the theoretical yield of methyl hydroxide produced by 1.2 tons of hydrogen gas. At the same time, the amount of CO left even after the completion of the reaction.
Related: Complete process of a metal displacement reaction in an aqueous medium with different examples.
It is clear from the problem that the limiting reactant is hydrogen since CO is still present in excess amounts after the end of the reaction. Now, let's find the molar masses of each entity of the reaction medium, such as
Molar mass of CO2 = 28g
Molar mass of 2H = 4g
Molar mass of CH3OH = 28+4 = 32g
In the final step, multiply the actual mass (used) of hydrogen with the molar mass ratio of the final product and limiting reagent such as
1.2 tons 2H2 = 32g CH3OH ÷ 4g 2H2 = 9.6 tons
Thus, the theoretical yield of methyl hydroxide produced from 1.2 tons of hydrogen is 9.6 tons.
- Finding theoretical yield at smaller levels
- Finding theoretical yield at the industrial level
Step 4: Add the Values in the Percent Yield Formula
Suppose you have been asked to calculate the percent yield of a reaction whose theoretical yield is 95g while the actual yield is 92.2g. To get percent yield, insert the values in the percent yield formula, So the percent yield equation will be
Percent yield = Theoretical yield ÷ Actual yield × 100
Percent yield = 92.2g ÷ 95g × 100 = 97.0%
Related: A detailed article to learn about history and importance of periodic table.
Importance of Percent Yield
Percent yield shows the efficiency of a chemical reaction or a complex chemical reaction. A company that manufactures different chemical compounds determines whether a reaction is profitable or not using percent yield definition.
For example, a chemical reaction possessing a low percent yield will not be favorable since the company has to spend more money to purchase the reactants than the amount it would earn from selling the resulting product. In a nutshell, lower productivity rates waste both money and time, which can even destroy a well-established enterprise in just a few months.
I hope this article helped you a lot in learn some useful things regarding different kinds of yield. There are also many useful articles in the blog section which you can read. Find the article and learn how to determine head of combustion in organic chemistry.