Practice Problem: Limiting Reagent and Percent Yield

Professor Dave Explains

1 Feb 201909:08

EducationalLearning

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TLDRThis educational video script guides viewers through a chemistry problem involving limiting reagents, theoretical yield, and percent yield. It explains the process of converting mass to moles, identifying silicon as the limiting reagent in a reaction with nitrogen, calculating the theoretical yield of Si3N4, and determining the percent yield based on the actual amount of product obtained. The script encourages viewers to consult a tutorial for a deeper understanding and provides a step-by-step approach to solving the problem.

Takeaways

🧪 Convert masses of reactants to moles to understand the reaction, as mass alone doesn't account for different molar masses of substances.
📐 Use the molar mass of silicon (28.09 g/mol) and nitrogen (28.01 g/mol for N2) to find the number of moles of each reactant.
🔍 Determine the limiting reagent by comparing the stoichiometric ratios, not just by the amount of substance present.
🤔 Remember, the limiting reagent is not necessarily the one in the lesser amount; it depends on the reaction's stoichiometry.
⚖️ Calculate the required moles of the other reactant based on the stoichiometry of the limiting reagent to confirm which is limiting.
📉 Silicon is identified as the limiting reagent in this reaction because it would run out before all nitrogen could react.
📚 The theoretical yield is calculated using the moles of the limiting reagent and the stoichiometric coefficients.
📝 To find the theoretical yield in grams, multiply the moles of product by the molar mass of the product (Si3N4 = 140.28 g/mol).
📊 The actual yield is the amount of product actually obtained from the reaction, in this case, 2.89 grams.
📈 Percent yield is calculated by dividing the actual yield by the theoretical yield and multiplying by 100 to get a percentage.
💯 The percent yield for this reaction is 87.0%, indicating the efficiency of the reaction in converting the limiting reagent to product.

Q & A

What is the first step in determining the limiting reagent in a chemical reaction?
-The first step is to convert the masses of the reactants into moles, as reactions occur according to stoichiometry and molar masses vary between substances.
How do you calculate the moles of a substance given its mass and molar mass?
-You calculate the moles by dividing the mass of the substance by its molar mass. For example, moles of silicon = mass of silicon (in grams) / molar mass of silicon.
Why can't you determine the limiting reagent by just looking at the amount of substance present?
-Because the limiting reagent is not necessarily the substance present in the lesser amount; it depends on the stoichiometric coefficients of the balanced chemical equation.
How does the stoichiometric ratio affect the determination of the limiting reagent?
-The stoichiometric ratio indicates the proportion in which reactants are consumed in a reaction. It helps determine which reactant will be completely consumed first, thus identifying the limiting reagent.
What is the theoretical yield in the context of a chemical reaction?
-The theoretical yield is the maximum amount of product that can be formed if all of the limiting reagent is completely converted into the product.
How do you calculate the theoretical yield of a reaction?
-You calculate the theoretical yield by using the moles of the limiting reagent and the stoichiometric coefficients from the balanced chemical equation to find the moles of product, then convert that to grams using the molar mass of the product.
What is the percent yield, and how is it calculated?
-The percent yield is a measure of the actual yield of a reaction compared to its theoretical yield, expressed as a percentage. It is calculated as (actual yield / theoretical yield) * 100.
Why is it important to know the molar mass of the product when calculating the theoretical yield?
-Knowing the molar mass of the product allows you to convert the moles of product, which is obtained from stoichiometric calculations, into grams to express the yield in a practical unit.
How can you verify that a reactant is the limiting reagent by using the product formation?
-You can verify by calculating the amount of product that could be formed from each reactant if they were the limiting reagent. The reactant that results in less product formation is the limiting reagent.
What is the significance of the molar mass of Si3N4 in calculating the theoretical yield of the reaction?
-The molar mass of Si3N4 is crucial because it allows you to convert the moles of product, which is calculated based on the limiting reagent, into grams to determine the theoretical yield of the reaction.
In the given reaction, how do you determine that silicon is the limiting reagent?
-You determine that silicon is the limiting reagent by comparing the amount of nitrogen needed to react completely with the available silicon and vice versa, using stoichiometric ratios, and by calculating the potential product formation from each reactant.

Outlines

00:00

🧪 Limiting Reagent and Theoretical Yield Calculation

This paragraph introduces a chemistry problem involving the calculation of the limiting reagent, theoretical yield, and percent yield for a reaction between silicon and nitrogen. The speaker emphasizes the importance of converting mass to moles due to different molar masses of substances and the stoichiometry of reactions. The process of determining the limiting reagent is explained through two methods: comparing the required moles of one reactant to the available moles of the other, and calculating the potential product formation from each reactant. Silicon is identified as the limiting reagent, and the theoretical yield is calculated based on the stoichiometry of the reaction and the molar mass of the product, Si3N4.

05:05

📊 Percent Yield and Reaction Analysis

The second paragraph continues the discussion on the chemistry problem by focusing on the calculation of the percent yield. It reiterates the identification of silicon as the limiting reagent and uses this information to determine the theoretical yield of the product in grams. The actual yield of the reaction is given as 2.89 grams, and the percent yield is calculated by dividing the actual yield by the theoretical yield and multiplying by 100, resulting in an 87.0% yield. The paragraph reinforces the concept of theoretical yield as the maximum possible product formation from the limiting reagent and provides a clear example of how to calculate and interpret percent yield in a chemical reaction.

Mindmap

Keywords

💡Limiting Reagent

The limiting reagent is the substance that is completely consumed during a chemical reaction and determines the maximum amount of product that can be formed. In the video, the concept is central to solving the problem, as it helps identify which reactant will run out first and thus limit the reaction's progress. Silicon is identified as the limiting reagent because there is not enough of it to react completely with the available nitrogen.

💡Theoretical Yield

The theoretical yield is the maximum amount of product that can be produced in a chemical reaction based on the stoichiometry of the balanced equation and the limiting reagent. It is an important concept in the script, as it represents the expected amount of product if the reaction goes to completion with 100% efficiency. The script calculates the theoretical yield of Si3N4 as 3.32 grams based on the moles of silicon used.

💡Percent Yield

Percent yield is a measure of the actual yield of a reaction compared to the theoretical yield, expressed as a percentage. It reflects the efficiency of a chemical reaction and accounts for any side reactions or losses. In the video, the percent yield is calculated by dividing the actual yield (2.89 grams) by the theoretical yield (3.32 grams) and multiplying by 100, resulting in an 87.0% yield.

💡Stoichiometry

Stoichiometry is the quantitative relationship between the amounts of reactants and products in a chemical reaction, as determined by the balanced chemical equation. The script uses stoichiometry to determine the limiting reagent and to calculate the theoretical yield, by comparing the molar ratios of the reactants to the product.

💡Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is used in the script to convert the mass of reactants into moles, which is necessary for understanding the reaction's stoichiometry. The molar masses of silicon and nitrogen are used to find out how many moles of each reactant are present in the given masses.

💡Moles

Moles are a unit of measurement used in chemistry to express amounts of a chemical substance, based on Avogadro's number. In the script, moles are calculated from the given masses of silicon and nitrogen to determine the quantities of reactants and to find the limiting reagent.

💡Reaction

A reaction in the script refers to the chemical process where two or more substances interact to form one or more new substances. The specific reaction discussed involves silicon and nitrogen combining to form Si3N4, and the script focuses on the limiting factors that affect the yield of this reaction.

💡Actual Yield

Actual yield is the amount of product that is actually obtained from a chemical reaction, which may be less than the theoretical yield due to inefficiencies or side reactions. In the script, the actual yield of 2.89 grams is compared to the theoretical yield to calculate the percent yield.

💡Balanced Equation

A balanced chemical equation is an equation that accurately represents the reactants and products in a chemical reaction with the correct stoichiometric coefficients, ensuring that the number of atoms of each element is the same on both sides of the equation. The script uses the balanced equation to determine the stoichiometric ratios needed for the calculations.

💡Stoichiometric Coefficients

Stoichiometric coefficients are numerical values that indicate the relative amounts of reactants and products in a balanced chemical equation. In the script, these coefficients are used to calculate the moles of reactants needed for the reaction or the moles of product that can be formed from the limiting reagent.

💡Tutorial

A tutorial in the script refers to an instructional guide or video that explains a concept or process in detail. The script mentions a tutorial on limiting reagents and percent yield, suggesting that viewers can refer to it for further clarification on these topics.

Highlights

The problem involves determining the limiting reagent, theoretical yield, and percent yield in a chemical reaction.

The importance of converting mass to moles for stoichiometric calculations is emphasized.

Molar masses of silicon and nitrogen are used to calculate the number of moles.

Stoichiometric coefficients are crucial for identifying the limiting reagent.

A method to find the limiting reagent by comparing the required moles of one reactant to the available moles of another.

Silicon is identified as the limiting reagent based on stoichiometric calculations.

The theoretical yield is calculated using the moles of the limiting reagent.

The molar mass of Si3N4 is used to convert moles of product to grams for theoretical yield.

The actual yield is compared to the theoretical yield to calculate the percent yield.

An 87.0% percent yield is calculated for the reaction.

The tutorial on limiting reagents and percent yield is recommended for further clarification.

The concept that the substance in lesser amount is not necessarily the limiting reagent is explained.

The tutorial uses the analogy of bologna sandwiches to explain the concept of limiting reagents.

Two methods are presented to determine the limiting reagent: comparing reactant needs and potential product formation.

The process of converting moles of product to grams using the molar mass of the product is detailed.

The importance of using significant figures in scientific calculations is highlighted.

Transcripts

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Takeaways

Q & A

What is the first step in determining the limiting reagent in a chemical reaction?

How do you calculate the moles of a substance given its mass and molar mass?

Why can't you determine the limiting reagent by just looking at the amount of substance present?

How does the stoichiometric ratio affect the determination of the limiting reagent?

What is the theoretical yield in the context of a chemical reaction?

How do you calculate the theoretical yield of a reaction?

What is the percent yield, and how is it calculated?

Why is it important to know the molar mass of the product when calculating the theoretical yield?

How can you verify that a reactant is the limiting reagent by using the product formation?

What is the significance of the molar mass of Si3N4 in calculating the theoretical yield of the reaction?

In the given reaction, how do you determine that silicon is the limiting reagent?