Lesson plan of Stoichiometry: Limiting and Excess

Objectives (5-10 minutes)

1. Understand the concept of limiting and excess reactants:

   • Students should be able to define limiting reactant and excess reactant in a chemical reaction.
   • They should understand how to identify the limiting reactant and excess reactant in a chemical reaction.

2. Apply the concept of limiting and excess reactants to solve stoichiometry problems:

   • Students should be able to use the concept of limiting and excess reactants to calculate the amount of product formed in a chemical reaction.
   • They should be able to solve problems involving the calculation of the amount of reactants needed and products formed, given the stoichiometric coefficients of the reaction.

3. Develop critical thinking and problem-solving skills:

   • Students should be able to apply the knowledge gained to solve practical problems.
   • They should be able to analyze different scenarios and identify the limiting and excess reactants in each.

Sub-objectives:

• Encourage active student participation in class by promoting discussions and questions about the content.
• Foster student autonomy in solving problems by encouraging them to seek solutions independently.
• Develop students' communication skills by explaining their reasoning and solutions to problems.

Introduction (10-15 minutes)

1. Review of previous content:

   • The teacher should recall the basic concepts of stoichiometry, including the concept of the mole, molar mass, and the relationship between mass, moles, and the number of particles. This is crucial for students to be able to properly understand the concept of limiting and excess reactants.
   • The teacher can start the class with some quick questions or a short exercise to assess students' prior knowledge of stoichiometry.

2. Problem situation:

   • The teacher can present two problem situations that illustrate the importance of the concept of limiting and excess reactants. For example:
     • If you have 3 eggs, 2 cups of flour, and 1 cup of milk, how many pancakes can you make? (The egg is the limiting reactant, as you cannot have more pancakes than the number of eggs available.)
     • If you have 10 g of iron and 15 g of oxygen, how much iron(III) oxide can you produce? (The iron is the limiting reactant, as you cannot form more iron oxide than the amount of iron available.)

3. Contextualization:

   • The teacher should highlight the importance of stoichiometry in everyday life and in different areas of science and industry. For example, stoichiometry is essential for the production of medicines, food, fuels, and construction materials.
   • The teacher can mention that stoichiometry is also used to determine the chemical composition of unknown substances, which is crucial in forensic investigations and in the analysis of samples in laboratories.

4. Getting students' attention:

   • The teacher can share some curiosities about stoichiometry, such as the fact that the perfume industry uses stoichiometry to ensure that fragrances are produced in the correct proportions and that a bomb explosion is a dramatic example of a chemical reaction that occurs when reactants are in excess.
   • The teacher can also make a connection to students' reality by explaining that stoichiometry is used in the production of food that they consume (for example, in baking) and in the production of medicines that they may have recently taken.

Development (20-25 minutes)

1. Presentation of the Theory (10-12 minutes)

   • The teacher should start the presentation of the theory by explaining what a limiting reactant and an excess reactant are.
   • They should provide examples and make analogies to facilitate students' understanding. For example, a chemical reaction can be compared to preparing a cake recipe, where each ingredient is a reactant and the cake is the product. If you have fewer eggs than the recipe calls for, the eggs are the limiting reactant and you will not be able to make more cakes than the number of eggs you have. If you have more flour than the recipe calls for, the flour is the excess reactant and no matter how many cups of flour you add, you will only be able to make the number of cakes that is determined by the number of eggs.
   • The teacher should explain that, to determine which is the limiting and which is the excess reactant in a chemical reaction, it is necessary to use the law of definite proportions, which is one of the bases of stoichiometry. They should show how to use the stoichiometric coefficients of the reaction to make these calculations.
   • The teacher should then explain how to calculate the amount of product formed in a chemical reaction when the limiting reactant is present in insufficient quantity. They should work through several examples to illustrate the application of this concept.

2. Problem Solving (10-13 minutes)

   • After presenting the theory, the teacher should move on to problem solving. They should start with simple problems and gradually increase the complexity.
   • The teacher should explain the step-by-step process for solving each problem, highlighting the key points and common pitfalls. They should encourage students to ask questions and discuss their solutions.
   • The teacher should provide immediate feedback and correct any conceptual errors. They should emphasize the importance of understanding the concept behind the problem, rather than simply applying a formula or method.
   • The teacher should vary the types of problems, including problems that require the identification of the limiting and excess reactants, as well as problems that involve the calculation of the amount of product formed.

3. Practical Activity (5-7 minutes)

   • To consolidate the knowledge acquired, the teacher should propose a practical activity.
   • They can, for example, provide students with a series of chemical reactions and ask them to identify the limiting and excess reactants in each one, as well as to calculate the amount of product formed.
   • The teacher should encourage students to work in groups and discuss their solutions. They should circulate around the room, offering help when needed and providing feedback on students' work.

Feedback (10-12 minutes)

1. Group Discussion (5-6 minutes)

   • The teacher should divide the students into groups and ask them to discuss the solutions or conclusions they reached during the practical activity.
   • Each group should then share their findings with the class.
   • The teacher should stimulate the discussion by asking questions to check students' understanding and to promote deeper reflection on the topic of the class.
   • The teacher should also take this opportunity to correct any misunderstandings and to reinforce the key concepts.

2. Connection with the Theory (2-3 minutes)

   • The teacher should make the connection between the practical activity and the theory presented in class.
   • They should explain how the concept of limiting and excess reactants was applied in the practical activity and how this relates to the calculation of the amount of product formed in a chemical reaction.
   • The teacher can do a quick review of the steps for solving stoichiometry problems and reinforce the importance of understanding the concept behind the problem, rather than simply applying a formula or method.

3. Final Reflection (3-4 minutes)

   • The teacher should propose that students reflect individually on what they learned in class.
   • They can ask questions such as: "What was the most important concept you learned today?" and "What questions are still unanswered?"
   • Students should write down their answers in a notebook or piece of paper.
   • After the reflection, the teacher can ask some students to share their answers with the class.
   • The teacher should conclude the class by reinforcing the Learning Objectives and encouraging students to continue exploring the topic outside of the classroom.

4. Feedback and Assessment (Optional)

   • If there is time, the teacher can ask for feedback from students on the class.
   • They can ask what they found most useful, what they found most challenging, and what they would like to learn more about the topic.
   • The teacher can use this feedback to adjust the teaching approach for future classes.
   • The teacher can also assess students' progress through observation during the class, the group discussions, and the practical activity, and provide individualized feedback to students if necessary.

Conclusion (5-7 minutes)

1. Recapitulation (2-3 minutes)

   • The teacher should start the Conclusion by summarizing the main points covered in class. They should review the concept of limiting and excess reactants, the importance of stoichiometry in solving chemical problems, and the method for calculating the amount of product formed in a chemical reaction.
   • They can do a brief review of the examples and problem situations discussed during the class to reinforce the practical application of the concept of limiting and excess reactants.

2. Theory-Practice Connection (1-2 minutes)

   • The teacher should then highlight how the class connected theory to practice. They should explain how understanding the concept of limiting and excess reactants allows scientists to predict the amount of products that will be formed in a chemical reaction, which is crucial in industry and many other fields.
   • They can recall the practical activity carried out during the class and how it helped students to apply and solidify the theoretical knowledge acquired.

3. Extra Materials (1-2 minutes)

   • The teacher should suggest extra materials for students who wish to deepen their knowledge on the topic. These materials can include textbooks, chemistry websites, educational videos, and apps for solving stoichiometry problems.
   • They can also suggest some additional exercises for students to practice at home, so that they can feel more confident when solving limiting and excess reactant problems.

4. Relevance of the Subject (1 minute)

   • Finally, the teacher should reinforce the importance of the topic to students' everyday lives. They can mention some examples of how stoichiometry is used in everyday life, such as in the production of food, medicines, construction materials, and cleaning products.
   • They can also emphasize that the ability to solve stoichiometry problems is not only useful in chemistry, but also in other areas of science and life, where the ability to predict and calculate quantities is essential.