Embedded Files
Lesson Instructions
Lesson Instructions
Review the learning goals and success criteria for Topic 5b: The Limiting Reactant.
Review the minds on, action, and consolidation sections of the lesson, completing any tasks as outlined.
Complete the fill-in-the-blanks handouts that have been provided to you. They have been linked below.
Practice and apply what you've learned by completing the practice tasks outlined at the end of the lesson.
Learning Goals
Learning Goals
I am learning to ...
Predict how the limiting reactant affects the amount of product that is made in a chemical reaction.
Success Criteria
Success Criteria
I am able to ...
Solve stoichiometry problems involving limiting and excess reactants.
Analyze practical applications of limiting and excess reactants.
By the end of this lesson, you should be able to answer the following question ...
What determines the amount of product made in a chemical reaction?
What determines the amount of product made in a chemical reaction?
Why is this an important question to answer?
In a chemical reaction, the amount of product made is dependent upon the amount of reactants available.
One or more reactants are completely used up in the reaction.
We will learn how stoichiometric calculations can be used to determine which reactants will limit the amount of product made.
Minds On
Minds On
The Limiting Reactant and .... S'mores?
The Limiting Reactant and .... S'mores?
Yes! You read that right. We're going to use s'mores to help us understand the concept of the limiting react and the excess reactant. Watch the following video explaining the stoichiometry of s'more-making. Once you have finished watching the video, you will navigate to D2L and, in your own words, define the limiting and excess reactant on the discussion page.
ON D2L-BRIGHTSPACE - In your own words, define the limiting reactant and the excess reactant. Textbook, google and wikipedia definitions are not permitted. I would like you to explain these terms in your own words. You can use an example to help your explanation (4 Marks - Communication).
Action
Action
Why is the limiting reactant important?
Why is the limiting reactant important?
In a chemical reaction, the amount of product formed is dependent upon the amount of reactants that are available.
One or more reactants are completey used up in the reaction.
Let's see how stoichiometric calculations can be used to determine which reactant will limit the amount of product made.
IF MR. CHRISTIE HAS 300 COOKIE OUTSIDES AND 100 CREAM INSIDES, HOW MANY OREO COOKIES COULD HE MAKE?
IF MR. CHRISTIE HAS 300 COOKIE OUTSIDES AND 100 CREAM INSIDES, HOW MANY OREO COOKIES COULD HE MAKE?
The balanced cookie equation for the production of an OREO cookie is:
2 COOKIE OUTSIDES + 1 CREAM INSIDE → 1 OREO
2 COOKIE OUTSIDES + 1 CREAM INSIDE → 1 OREO
Figure 1. The chemistry of Mr. Christie's OREO cookies.
With 300 cookie outsides, we could make 150 oreos (300 cookie outsides divided by 2 require for each = 150).
With 100 cream insides, he could make 100 oreos (1 cream inside per oreo).
Therefore, the number of OREOs he can produce is LIMITED by the amount of cream insides he has.
Therefore the cream insides are the limiting reactant.
The cookie outsides are the excess reactant.
To produce 100 OREOs, Mr. Christie would need: 200 cookie outsides & 100 cream insides.
There will be 100 excess cookie outsides left over, and 100 OREOs will be produced.
These types of problems are very similar to the ones encountered in chemistry.
In a chemical reaction, it is impossible to get the exact number of atoms reacting. One of the reactants is always in excess to make sure the required amount of product is obtained.
The reactant that is added in excess is:
The least expensive reactant
The most readily available reactant
Purchases in stock supply
Easy to remove
Controlling the limiting and excess reagents in a chemical reaction has important consumer, healthy, and environmental applications.
The Limiting Reactant
The Limiting Reactant
The LR is the substance that is totally consumed when the chemical reaction is complete.
The amount of product formed is limited by the LR since the reaction cannot proceed without it.
Therefore, the reactant that runs out first is called the limiting reactant because it controls or limits when the reaction stops.
The Excess Reactant
The Excess Reactant
The ER is the reactant with a greater amount than necessary to react completely with the LR.
It is the the reactant that remains after a chemical reaction is complete.
Therefore, the reactant that is not used up once the reaction has stopped is called the excess reactant.
Figure 2. The RED reactant is limiting how much product can be formed. the GREEN reactant is found in excess.
Figure 3. Three moles of nitrogen reacting with six moles of hydrogen.
For a chemist, the balanced chemical equation is the recipe that must be followed. In Lesson 5a you saw a reaction in which nitrogen gas is combined with hydrogen gas to form ammonia. The balanced equation is shown below.
N2(g)+3H2(g)→2NH3(g)
N2(g)+3H2(g)→2NH3(g)
We know that the coefficients of the balanced equation tell us the mole ratio that is required for this reaction to occur. One mole of N2 will react with three moles of H2 to form two moles of NH3.
Now let us suppose that a chemist were to react three moles of nitrogen with six moles of hydrogen.
So what happened in this reaction? The limiting reactant (or limiting reagent) is the reactant that determines the amount of product that can be formed in a chemical reaction. The reaction proceeds until the limiting reactant is completely used up. In our example above, the hydrogen is the limiting reactant. The excess reactant (or excess reagent) is the reactant that is initially present in a greater amount than will eventually be reacted. In other words, there is always excess reactant left over after the reaction is complete. In the above example, the nitrogen is the excess reactant.
Limiting and Excess Reactant - Calculations
Limiting and Excess Reactant - Calculations
Example 1.
Example 1.
What is the limiting reactant in the following reaction if 5.0 mol of hydrogen gas is added to 2.3 mol of oxygen gas?
Example 2.
Example 2.
A 35.0 g sample of phosphorus (P) reacts with 28.0 g of oxygen gas (O2) according the following reaction?
a) What is the limiting reactant?
b) How many grams of diphosphorus pentoxide (P2O5) are formed?
Example 3.
Example 3.
How many grams of NH3 can be produced from the reaction of 28 grams of N2 and 25 grams of H2 ?
Example 4.
Example 4.
Calculate the mass of silver chromate that forms when 50.0 mL of a 0.100 mol/L silver nitrate reacts with 25.0 mL of 0.150 mol/L sodium chromate.
Consolidation
Consolidation
(1) Defining the LR and ER:
ON D2L-BRIGHTSPACE - In your own words, define the limiting reactant and the excess reactant. Textbook, google and wikipedia definitions are not permitted. I would like you to explain these terms in your own words. You can use an example to help your explanation (4 Marks - Communication).
(2) Complete the following practice questions using your textbook.
Page 223 #12-13, 225 #1, 2, 7, 10
(3) Complete the Lesson 5b Concept Check on D2L - Brightspace.
This lesson is now complete. Return to D2L - Brightspace and complete the assigned tasks to consolidate your learning.
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