Introduction
Percentage yield is a concept that is widely used in chemistry, particularly in chemical reactions. It is an essential concept that helps to determine the efficiency of a chemical reaction. In this blog post, we will explore what percentage yield is, how to calculate it, and some examples of how it is used.
What is Percentage Yield?
The efficiency of a chemical reaction can be quantified using a measure known as the percentage yield. It is the percentage of the theoretical yield that is obtained in a chemical reaction. The theoretical yield is the maximum amount of product that can be obtained from a reaction, assuming that all of the reactants are consumed and that the reaction goes to completion. The actual yield, on the other hand, is the amount of product that is obtained in a reaction.
Calculating Percentage Yield
The formula for calculating percentage yield is straightforward:
Percentage Yield = (Actual Yield / Theoretical Yield) x 100%
To calculate percentage yield, you need to know the actual yield and the theoretical yield of the reaction. The actual yield is the amount of product that is obtained in the reaction, while the theoretical yield is the maximum amount of product that can be obtained.
Example 1:
Suppose you want to prepare 5.00 g of water from the reaction between hydrogen gas and oxygen gas. This reaction can be represented by the balanced chemical equation:
2H2(g) + O2(g) → 2H2O(l)
The molar mass of water is 18.015 g/mol. To calculate the theoretical yield, you need to use stoichiometry to determine the amount of water that can be produced from a given amount of hydrogen and oxygen. The balanced equation shows that two moles of hydrogen react with one mole of oxygen to produce two moles of water. Therefore, the theoretical yield of water can be calculated as follows:
Theoretical Yield = (5.00 g H2 / 2.016 g/mol H2) x (1 mol O2 / 2 mol H2) x (2 mol H2O / 1 mol O2) x (18.015 g/mol H2O) = 44.7 g H2O
Suppose that you actually obtained 3.50 g of water. To calculate the percentage yield, you would use the formula:
Percentage Yield = (Actual Yield / Theoretical Yield) x 100%
Percentage Yield = (3.50 g / 44.7 g) x 100% = 7.83%
This means that the reaction was only 7.83% efficient, and most of the reactants were wasted.
Example 2:
Suppose you want to prepare 10.0 g of calcium chloride from the reaction between calcium carbonate and hydrochloric acid. This reaction can be represented by the balanced chemical equation:
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
The molar mass of calcium chloride is 110.98 grams per mole. To calculate the theoretical yield, you need to use stoichiometry to determine the amount of calcium chloride that can be produced from a given amount of calcium carbonate and hydrochloric acid. The balanced equation shows that one mole of calcium carbonate reacts with two moles of hydrochloric acid to produce one mole of calcium chloride. Therefore, the theoretical yield of calcium chloride can be calculated as follows:
Theoretical Yield = (10.0 g CaCO3 / 100.09 g/mol CaCO3) x (1 mol CaCO3 / 1 mol CaCl2) x (110.98 g/mol CaCl2) = 11.1 g CaCl2
Suppose that you actually obtained 9.50 g of calcium chloride. To calculate the percentage yield of this reaction, you can use the formula:
Percentage Yield = (Actual Yield/Theoretical Yield) x 100
In this case, the actual yield is 9.50 g, and the theoretical yield is 10.67 g. By substituting these values into the formula, the resulting expression is:
Percentage Yield = (9.50/10.67) x 100
Percentage Yield = 88.98%
So the percentage yield of the reaction is 88.98%.
Factors Affecting Percentage Yield
The percentage yield of a reaction is affected by several factors. One of the most important factors is the purity of the reactants. If the reactants are impure, the yield of the reaction will be lower than the theoretical yield. This is because impurities in the reactants can interfere with the reaction and reduce the amount of product that is formed.
Another factor that can affect the percentage yield is the reaction conditions. For example, if the temperature or pressure is not optimal for the reaction, the yield of the reaction may be lower than expected. Similarly, if the reaction time is too short, the yield may be lower because the reaction has not had enough time to go to completion.
In addition, the stoichiometry of the reaction can affect the percentage yield. If the stoichiometry is not exact, some of the reactants may be left over after the reaction is complete, reducing the yield of the reaction. This can happen, for example, if one of the reactants is added in excess or if the reaction is not allowed to proceed to completion.
Examples of Percentage Yield in Everyday Life
Percentage yield is an important concept in many fields, including chemistry, engineering, and manufacturing. Here are some examples of how percentage yield is used in everyday life:
Food Production
The percentage yield is an important factor in the food production industry. For example, when making bread, the percentage yield is calculated to determine how much bread can be made from a given amount of flour. The percentage yield is affected by factors such as the quality of the flour, the temperature and humidity of the environment, and the mixing and kneading process.
Pharmaceutical Manufacturing
The pharmaceutical industry relies on the concept of percentage yield to ensure that drugs are produced efficiently and cost-effectively. The percentage yield is calculated for each step of the manufacturing process to identify areas where the yield can be improved. By optimizing the percentage yield, pharmaceutical companies can reduce the cost of production and improve the availability of drugs to patients.
Chemical Engineering
Percentage yield is an important concept in chemical engineering. It is used to optimize the production of chemicals and materials, such as plastics, fuels, and fertilizers. By maximizing the percentage yield, chemical engineers can reduce the cost of production and minimize the waste generated by the process.
Solar Energy
The efficiency of solar cells is often measured in terms of percentage yield. The percentage yield of a solar cell refers to the percentage of sunlight that is converted into electrical energy. By improving the percentage yield of solar cells, scientists and engineers can improve the efficiency of solar energy and make it more cost-effective.
Summary
Percentage yield is a crucial concept in chemistry and many other fields. It allows scientists, engineers, and manufacturers to calculate the efficiency of a reaction or process and identify areas where improvements can be made. By optimizing the percentage yield, it is possible to reduce the cost of production, minimize waste, and improve the availability of products and services.