Limiting Reactant and Percent Yield Practice

Oct 13, 2025 by thesweetdesigns.com 90 views

Limiting Reactant and Percent Yield Practice

Understanding the Concept of Limiting Reactant

In a chemical reaction, the limiting reagent is the reactant that is consumed first, and it determines the maximum amount of product that can be formed. In this practice problem, we will use the reaction between sodium (Na) and chlorine gas (Cl2) to form sodium chloride (NaCl).

The Balanced Chemical Equation

The balanced chemical equation for the reaction is:

\text{Na} (s) + \text{Cl}_2 (g) \rightarrow \text{NaCl} (s)

Given Information

We are given the following information:

6.70 moles of Na react with 3.20 moles of Cl2.

Step 1: Determine the Limiting Reactant

To determine the limiting reagent, we need to compare the mole ratio of the reactants to the coefficients in the balanced chemical equation. The balanced equation shows that 1 mole of Na reacts with 1 mole of Cl2 to form 1 mole of NaCl.

We can set up a table to compare the mole ratio of the reactants:

Reactant	Mole Ratio	Mole Amount
Na	1:1	6.70
Cl2	1:1	3.20

Since the mole ratio of Na to Cl2 is 1:1, we can see that the mole amount of Cl2 (3.20 moles) is less than the mole amount of Na (6.70 moles). Therefore, Cl2 is the limiting reagent.

Step 2: Calculate the Theoretical Yield

To calculate the theoretical yield, we need to use the mole ratio of the reactants to the coefficients in the balanced chemical equation. Since Cl2 is the limiting reagent, we will use the mole amount of Cl2 to calculate the theoretical yield.

The balanced equation shows that 1 mole of Cl2 produces 1 mole of NaCl. Therefore, the theoretical yield of NaCl is equal to the mole amount of Cl2:

Theoretical Yield (NaCl) = Mole Amount of Cl2 = 3.20 moles

Step 3: Calculate the Percent Yield

To calculate the percent yield, we need to know the actual yield of NaCl. However, since we are not given the actual yield, we will assume that the actual yield is equal to the theoretical yield.

Percent Yield = (Actual Yield / Theoretical Yield) x 100%

Since the actual yield is equal to the theoretical yield, the percent yield is 100%:

Percent Yield = (3.20 moles / 3.20 moles) x 100% = 100%

Conclusion

In this practice problem, we determined that Cl2 is the limiting reagent in the reaction between Na and Cl2 to form NaCl. We then calculated the theoretical yield of NaCl and assumed that the actual yield is equal to the theoretical yield. Finally, we calculated the percent yield, which is 100%.

Discussion

This problem illustrates the concept of limiting reagent and how it affects the yield of a chemical reaction. The limiting reagent is the reactant that is consumed first, and it determines the maximum amount of product that can be formed. In this case, Cl2 is the limiting reagent, and it determines the maximum amount of NaCl that can be formed.

Practice Problems

In the reaction between H2 and O2 to form H2O, 2.50 moles of H2 react with 1.50 moles of O2. What is the limiting reagent?
In the reaction between Na and Cl2 to form NaCl, 4.00 moles of Na react with 2.00 moles of Cl2. What is the limiting reagent?
In the reaction between H2 and O2 to form H2O, 3.00 moles of H2 react with 2.00 moles of O2. What is the limiting reagent?

Answer Key

Additional Resources

For more practice problems and additional resources, please visit the following websites:

Khan Academy: Chemistry
Chemistry LibreTexts: Stoichiometry
Purdue University: Chemistry 125: Stoichiometry
Limiting Reactant and Percent Yield Practice: Q&A

Understanding the Concept of Limiting Reactant

In a chemical reaction, the limiting reagent is the reactant that is consumed first, and it determines the maximum amount of product that can be formed. In this Q&A article, we will use the reaction between sodium (Na) and chlorine gas (Cl2) to form sodium chloride (NaCl) to answer some common questions about limiting reagent and percent yield.

Q: What is the limiting reagent?

A: The limiting reagent is the reactant that is consumed first in a chemical reaction, and it determines the maximum amount of product that can be formed.

Q: How do I determine the limiting reagent?

A: To determine the limiting reagent, you need to compare the mole ratio of the reactants to the coefficients in the balanced chemical equation. You can set up a table to compare the mole ratio of the reactants and see which one is consumed first.

Q: What is the difference between the limiting reagent and the excess reagent?

A: The limiting reagent is the reactant that is consumed first, while the excess reagent is the reactant that is left over after the reaction is complete. The excess reagent does not affect the yield of the product.

Q: How do I calculate the theoretical yield?

A: To calculate the theoretical yield, you need to use the mole ratio of the reactants to the coefficients in the balanced chemical equation. You can use the mole amount of the limiting reagent to calculate the theoretical yield.

Q: What is the difference between the theoretical yield and the actual yield?

A: The theoretical yield is the maximum amount of product that can be formed, while the actual yield is the amount of product that is actually formed. The actual yield is usually less than the theoretical yield due to factors such as impurities and equipment limitations.

Q: How do I calculate the percent yield?

A: To calculate the percent yield, you need to divide the actual yield by the theoretical yield and multiply by 100%. This will give you the percentage of the theoretical yield that is actually formed.

Q: What is the significance of percent yield?

A: Percent yield is a measure of the efficiency of a chemical reaction. A high percent yield indicates that the reaction is efficient and that most of the reactants are converted to products.

Q: Can you give an example of how to calculate the percent yield?

A: Let's say we have a reaction between Na and Cl2 to form NaCl, and we have 6.70 moles of Na and 3.20 moles of Cl2. We determine that Cl2 is the limiting reagent and calculate the theoretical yield to be 3.20 moles of NaCl. If the actual yield is 2.50 moles of NaCl, then the percent yield is:

Percent Yield = (2.50 moles / 3.20 moles) x 100% = 78.1%

Q: What are some common mistakes to avoid when calculating percent yield?

A: Some common mistakes to avoid when calculating percent yield include:

Not using the correct mole ratio of the reactants
Not calculating the theoretical yield correctly
Not using the correct actual yield
Not rounding the percent yield to the correct number of significant figures