Objectives (5 - 7 minutes)

1. Understand Hess's Law and its importance in solving thermochemical problems.

   • Explain Hess's Law, which states that the total energy change in a chemical reaction is independent of the path the reaction takes.
   • Demonstrate how Hess's Law can be used to determine the enthalpy change of a chemical reaction.

2. Apply Hess's Law to calculate the enthalpy change of a chemical reaction.

   • Perform practical exercises and problem-solving situations involving the application of Hess's Law.
   • Interpret the results obtained and relate them to the practical application of Hess's Law.

3. Relate Hess's Law to previous concepts of thermochemistry.

   • Review previously studied thermochemistry concepts, highlighting the relationship between them and Hess's Law.
   • Reinforce the idea that Hess's Law is a mathematical tool that allows us to calculate the enthalpy change of a reaction, regardless of the path taken.

Secondary Objectives:

• Stimulate students' critical and analytical thinking when solving problems involving Hess's Law.
• Promote group discussion and collaboration to solve problems, encouraging teamwork skills.
• Develop students' ability to relate theory to practice by applying the concepts studied to solve real problems.

Introduction (10 - 15 minutes)

1. Review of previous concepts: The teacher will start the lesson with a brief review of thermochemistry concepts already studied by the students. The concepts of enthalpy, endothermic and exothermic reactions, and the representation of reactions through chemical equations will be revisited. The goal is to ensure that all students have a solid foundation for understanding Hess's Law.

2. Problem-solving situation: The teacher will present two problem-solving situations that will be addressed throughout the lesson. The first situation will involve the combination of two chemical equations (reverse and direct), and the second will involve the use of a multiple chemical reaction. Both situations will require the application of Hess's Law to determine the enthalpy change.

3. Contextualization: The teacher will contextualize the importance of Hess's Law in the study of thermochemistry. It will be explained that Hess's Law allows the calculation of the enthalpy change of a chemical reaction, regardless of the path taken by the reaction, which is essential for understanding and predicting chemical reactions. The teacher may cite practical examples, such as the use of Hess's Law in the pharmaceutical industry for the synthesis of medications.

4. Introduction to the topic: To capture the students' interest, the teacher may present two curiosities related to Hess's Law. The first is that Hess's Law was formulated by the Swiss chemist Germain Hess in 1840 and is considered one of the cornerstones of modern thermochemistry. The second is that Hess's Law was fundamental for the discovery of nuclear fission, which led to the atomic bomb and nuclear energy.

5. Engaging students' attention: To conclude the Introduction and capture the students' attention, the teacher may propose two challenges. The first is to predict the final temperature of a mixture of water and salt, based on the enthalpy changes of the components' dissolutions. The second is to determine the enthalpy change of an unknown chemical reaction, based on known chemical reactions and Hess's Law. The teacher will emphasize that both challenges will be solved during the lesson, encouraging student participation and interest.

Development (20 - 25 minutes)

1. Theory Explanation (10 - 12 minutes)

   1.1. Presentation of Hess's Law: The teacher will start the theory explanation by presenting Hess's Law clearly and concisely. It will be highlighted that this law establishes that the total energy change in a chemical reaction is independent of the path the reaction takes.

   1.2. Explanation of the reaction path concept: The teacher will clarify what is meant by the reaction path, explaining that it is the sequence of chemical reactions necessary to convert the reactants into the final products.

   1.3. Demonstration of the application of Hess's Law: The teacher will demonstrate how Hess's Law can be applied to calculate the enthalpy change of a chemical reaction. Practical examples will be presented, where the teacher will show step by step how to combine two or more chemical equations to obtain the desired equation.

2. Resolution of Problem Situations (5 - 7 minutes)

   2.1. Using Hess's Law: The teacher will solve the problem situations presented in the Introduction using Hess's Law. They will explain each step of the process, from identifying the chemical reactions to be combined to determining the enthalpy change.

   2.2. Discussion of results: After solving the problem situations, the teacher will discuss the results obtained with the students, relating them to the theory presented. They will explain how the correct application of Hess's Law allowed for the precise determination of the enthalpy change.

3. Practical Activity (5 - 6 minutes)

   3.1. Application Exercise: The teacher will propose a practical exercise where students, in groups, will have to use Hess's Law to calculate the enthalpy change of a chemical reaction. The teacher will provide the necessary chemical equations and guide the students during the exercise.

   3.2. Discussion and Correction: After the exercise is completed, the teacher will discuss the solutions found by the groups, clarifying any doubts that may arise. They will also correct any errors, showing the students the importance of correctly applying Hess's Law.

This lesson Development will allow students to understand the theory of Hess's Law and know how to apply it to calculate the enthalpy change of a chemical reaction. In addition, solving the problem situations and the practical activity will allow students to see the practical application of Hess's Law and develop their problem-solving skills.

Return (8 - 10 minutes)

1. Group Discussion (3 - 4 minutes)

   • The teacher will propose a group discussion on the solutions found for the problem situations and the practical exercise.
   • Each group will have a maximum of 2 minutes to present their solutions and explain the reasoning used.
   • During the presentations, the teacher will encourage the participation of all students, asking questions that promote reflection and understanding of the topic.

2. Connection with Theory (2 - 3 minutes)

   • After the presentations, the teacher will make a connection between the solutions presented by the groups and the theory of Hess's Law.
   • The points where the correct application of Hess's Law was crucial for problem-solving will be highlighted.
   • The teacher will also correct any errors or misconceptions, reinforcing the correct concepts and clarifying any remaining doubts.

3. Individual Reflection (2 - 3 minutes)

   • To conclude, the teacher will suggest that students reflect individually on the lesson.
   • The following questions will be asked:
     1. What was the most important concept learned today?
     2. What questions have not been answered yet?
   • Students will have a minute to think and write down their answers.
   • After the given time, the teacher will ask some students to share their answers with the class, promoting a brief discussion.
   • The teacher will emphasize the importance of questioning and seeking answers, reinforcing that learning is a continuous process.

This Return will allow the teacher to assess students' progress in understanding Hess's Law and identify possible difficulties or gaps that need to be addressed in future lessons. Additionally, by promoting discussion and reflection, the teacher will be stimulating critical thinking and students' autonomy, essential skills for effective learning.

Conclusion (5 - 7 minutes)

1. Recapitulation (2 - 3 minutes)

   • The teacher will summarize the main points covered in the lesson, recalling the definition and application of Hess's Law in thermochemistry.
   • The concept that Hess's Law allows the calculation of the enthalpy change of a chemical reaction, regardless of the path taken by the reaction, will be reinforced.
   • A brief review of the steps necessary to apply Hess's Law will be made, including identifying the chemical reactions to be combined and determining the enthalpy change.

2. Connection between Theory, Practice, and Applications (1 - 2 minutes)

   • The teacher will emphasize how the lesson connected the theory of Hess's Law with the practice of solving thermochemical problems.
   • It will be highlighted that the correct application of Hess's Law allows for predicting and controlling the enthalpy variation in chemical reactions, which has practical applications in various fields, such as the pharmaceutical industry and energy production.
   • The teacher may cite specific examples of how Hess's Law is used in practice, reinforcing the relevance of the content learned.

3. Supplementary Material (1 - 2 minutes)

   • The teacher will suggest some materials for additional study, such as books, websites, videos, and apps, that deepen the understanding of Hess's Law and offer more practice exercises.
   • Students will be recommended to review the theory and practice problem-solving using the suggested materials to consolidate their learning of Hess's Law.

4. Importance of the Subject for Everyday Life (1 minute)

   • To conclude, the teacher will emphasize the importance of the subject learned for everyday life.
   • It will be explained that thermochemistry, which includes Hess's Law, is essential to understand and control many processes that occur around us, from food preparation to medication production and energy generation.
   • The teacher will encourage students to observe and question the chemical phenomena they encounter in daily life, using what they learned in the lesson to better understand these phenomena.

The Conclusion of the lesson will allow the teacher to reinforce the most important concepts, make connections to the real world, and suggest resources for autonomous study. Additionally, by highlighting the relevance of the subject for everyday life, the teacher will encourage students to apply what they learned in their lives and realize the importance of chemistry in their daily routines.