Limiting Reagents and Percentage Yield

Limiting Reagents and Percentage Yield

Introduction

• In an ideal experiment, we have the exact amount of each reactant needed to produce a product, and we end up with the exact amount of product we are supposed to

• This is not​ always the reality, we often deal with limiting reactants and wind up with less or more than we were supposed to

What is a Limiting Reactant?

• A limiting reactant is the reactant the limits how much of a product can be produced from a reactant.

• It is completely used up​ when the reaction takes place

• the reactant not used up is known as the excess reactant​

Solving for Limiting Reactant Example 1

Silicon dioxide reacts with hydrogen Fluoride in the following reaction​:

SiO₂​+4HF → SiF₄ + 2H₂O

If 6.0 mol HF is added to 4.5 mol SiO₂, Which is the limiting reactant?​

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• Step 1: Identify one of the products in the reaction to measure your production by. Let's use SiF_4, since it exists as one mole in the equation

• Step 2: Convert our given moles of reactants to moles of our products

Solving for Limiting Reactant Example 1

Silicon dioxide reacts with hydrogen Fluoride in the following reaction​:

SiO₂​+4HF → SiF₄ + 2H₂O

If 6.0 mol HF is added to 4.5 mol SiO₂, Which is the limiting reactant?​

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• Step 3: Identify which reactant makes less with the given amounts

• 6 mol HF can make 1.5 mol SiF₄

• 4.5 mol SiO₂ can make 4.5 mol of SiF₄

• Since HF can only make 1.5 mol, it is the limiting reagent

Solving for Limiting Reactant Example 2

Iron oxide is made in the lab by combining iron with steam in the following reaction

3 Fe + 4 H₂O→​Fe₃O₄ + 4 H₂

When 36 grams of H₂O is mixed with 67.0 grams of Fe, which is the limiting reagent?​

• Step 1: Pick a product to measure your yield by. Which Product is the easiest to work with?

Multiple Choice

In the equation

3 Fe + 4 H₂O→​Fe₃O₄ + 4 H_2,

Which product will give the simples ratio to calculate with?

• Fe₃O₄

• H₂

Solving for Limiting Reactant Example 2

Iron oxide is made in the lab by combining iron with steam in the following reaction

3 Fe + 4 H₂O→​Fe₃O₄ + 4 H₂

When 36 grams of H₂O is mixed with 67.0 grams of Fe, which is the limiting reagent?​

• Step 1: Pick a product to measure your yield by. We will use Fe₃O₄

• Step 2: Convert both reactants from grams to moles, then to moles of Fe₃O₄

Multiple Choice

Iron oxide is made in the lab by combining iron with steam in the following reaction

3 Fe + 4 H₂O→​Fe₃O₄ + 4 H₂

When 36 grams of H₂O is mixed with 67.0 grams of Fe, which is the limiting reagent?​

• Fe

• H₂O

Percentage Yield

• In equations we calculate the theoretical yield, or the maximum amount of a product that can be produced from a given amount

• In reality, it is hard to get the maximum amount for a variety of reasons

• The actual yield is the measured amount of a product in a reaction​

• To determine how efficient a reaction is, chemists use the following equation calculate the percentage yield​

Percentage Yield Practice Problem 1

​Chlorobenzene is a used in the production of a variety of chemicals. In order to be used, it is prepared with chlorine in the following equation:

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​When 36.8 g C₆H₆ react with an excess of Cl₂ the actual yield of C₆H₅Cl is 38.8 g. What is the Percentage Yield?

• Step 1: Set up your Stoichiometry Equation

• Step 2: Find the masses of C₆H₆ and C₆H₅Cl

• Step 3: Plug in your masses and solve​

Percentage Yield Practice Problem 1

​Chlorobenzene is a used in the production of a variety of chemicals. In order to be used, it is prepared with chlorine in the following equation:

​

​When 36.8 g C₆H₆ react with an excess of Cl₂ the actual yield of C₆H₅Cl is 38.8 g. What is the Percentage Yield?

• Step 1: Set up your Stoichiometry Equation

• Step 2: Find the masses of C₆H₆ and C₆H₅Cl

• Step 3: Plug in your masses and solve​ for Theoretical yield

Percentage Yield Practice Problem 1

​Chlorobenzene is a used in the production of a variety of chemicals. In order to be used, it is prepared with chlorine in the following equation:

​

​When 36.8 g C₆H₆ react with an excess of Cl₂ the actual yield of C₆H₅Cl is 38.8 g. What is the Percentage Yield?

• Step 1: Set up your Stoichiometry Equation

• Step 2: Find the masses of C₆H₆ and C₆H₅Cl

• Step 3: Plug in your masses and solve​ for Theoretical yield

• Step 4: solve for Percentage Yield​