Objectives (5 - 7 minutes)

1. Understand Hess's Law:

   • The teacher should ensure that students understand the fundamental concept of Hess's Law in thermochemistry.
   • Students should be able to explain Hess's Law in their own words and apply it to different chemical reaction scenarios.

2. Apply Hess's Law to calculate enthalpy change:

   • Students should be able to use Hess's Law to calculate the enthalpy change in different chemical reactions.
   • They should be able to identify the necessary data for these calculations and how to apply the formula correctly.

3. Develop problem-solving skills in thermochemistry:

   • Students should be able to apply their knowledge of Hess's Law to solve complex problems in thermochemistry.
   • They should be able to analyze different reaction scenarios and calculate the enthalpy change using Hess's Law.

Secondary objectives:

• Promote active participation in the classroom: The teacher should encourage active student participation through discussions and group problem-solving.
• Stimulate the connection of content with the real world: The teacher should provide practical examples of how Hess's Law is applied in everyday life or other areas of science.

Introduction (10 - 12 minutes)

1. Review of previous concepts:

   • The teacher should start the lesson by recalling the basic concepts of thermochemistry, such as enthalpy, heat of reaction, and the idea that enthalpy is a state function.
   • The notion of energy and how it relates to chemical reactions should also be reviewed.

2. Problem situations to spark interest:

   • The teacher can present the following problem situations to spark students' interest:
     • How can we determine the enthalpy change in a chemical reaction that cannot be measured directly?
     • How can we predict the amount of energy released or absorbed in a chemical reaction without performing it?

3. Contextualization of the importance of the topic:

   • The teacher should explain the importance of Hess's Law in thermochemistry, highlighting that it allows calculating the enthalpy of a reaction even when it cannot be measured directly.
   • It should also be mentioned that Hess's Law is widely used in the chemical industry to design and optimize chemical processes.

4. Presentation of the topic in an engaging way:

   • The teacher can present curiosities or applications of Hess's Law to capture students' attention, such as:
     • Hess's Law was formulated by the Swiss chemist Germain Hess in 1840 but was only recognized by the scientific community after the publication of the work of the German chemist Julius Thomsen in 1871.
     • Hess's Law can be used to explain why the burning of coal (an exothermic reaction) and photosynthesis (an endothermic reaction) are essential processes for life on Earth.

5. Introduction of the topic and gaining attention:

   • The teacher should then introduce the topic of Hess's Law, explaining that it allows calculating the enthalpy change of a chemical reaction from the enthalpies of previous reactions.
   • To gain students' attention, the teacher can show a simple chemical reaction experiment, such as mixing baking soda and vinegar, and ask if students can predict the amount of energy released in the reaction.
   • Then, the teacher can explain that Hess's Law allows us to do exactly that - predict the enthalpy of a reaction without performing it.

Development (20 - 25 minutes)

1. Modeling Activity: Concept Map Construction (10 - 12 minutes)

   • The class will be divided into groups of no more than 5 students. Each group will receive a large sheet of paper and colored markers.
   • The teacher will provide students with the necessary information for the construction of the concept map, such as the basic concepts of thermochemistry, the idea that enthalpy is a state function, and Hess's Law itself.
   • The groups should organize the concepts on the paper, making connections between them and adding practical examples whenever possible.
   • The teacher will circulate around the room, assisting the groups when necessary and clarifying doubts.
   • At the end of the activity, each group will present their concept map to the class, explaining the connections they made between the concepts.

2. Practical Activity: "Solving the Mystery of the Unknown Reaction" (10 - 12 minutes)

   • The teacher will prepare in advance a set of "reaction cards" - each card representing a chemical reaction, with the reactants and products indicated, but without the balanced chemical equation.
   • Each group of students will receive a set of reaction cards. The group's task will be to balance the chemical equations and then use Hess's Law to calculate the enthalpy change of each reaction.
   • Students should write down their balanced equations and enthalpy change calculations on a sheet of paper.
   • At the end of the activity, each group will present their balanced equations and enthalpy change calculations to the class. The teacher will check if the calculations are correct and clarify any doubts.

3. Group Discussion: Applications of Hess's Law (5 - 7 minutes)

   • After the conclusion of the activities, the teacher will lead a group discussion on the applications of Hess's Law in everyday life and the chemical industry.
   • The teacher can present examples of real situations where Hess's Law is used, such as determining the fat content in foods, optimizing industrial processes, or predicting the behavior of new materials.
   • Students will be encouraged to share their own ideas and experiences and to make connections between the theory learned and the real world.

Return (8 - 10 minutes)

1. Group Discussion: (3 - 4 minutes)

   • The teacher should invite each group to briefly share the solutions or conclusions they reached during the practical activity.
   • Each group will have a maximum of 3 minutes to present, ensuring that all groups have the opportunity to speak.
   • During the presentations, the teacher should ask questions to ensure that key concepts were understood and to clarify any misunderstandings.

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

   • After all groups have presented, the teacher should make the connection between the practical activities and the theory of Hess's Law.
   • The teacher should highlight how Hess's Law allows calculating the enthalpy change of a reaction from the enthalpies of previous reactions, and how this was applied during the activity.
   • The teacher should also reinforce the key concepts of Hess's Law, such as the idea that enthalpy is a state function, meaning it depends only on the initial and final states, regardless of the path taken.

3. Final Reflection: (2 - 3 minutes)

   • The teacher should propose that students reflect for a minute on the following questions:
     1. What was the most important concept learned today?
     2. What questions remain unanswered?
   • After a minute of reflection, the teacher should invite some students to share their answers with the class.
   • The teacher should note the unanswered questions and commit to addressing them in the next class or in future activities.

4. Feedback and Closure: (1 minute)

   • Finally, the teacher should thank the students for their participation and effort and encourage them to continue studying the subject.
   • The teacher should also ask for feedback from the students about the lesson, asking what they found most useful or interesting, and if there is anything they would like to see more of in future lessons.
   • The teacher should note the students' feedback and use it to improve future lessons.

Conclusion (5 - 7 minutes)

1. Summary of Covered Content: (2 - 3 minutes)

   • The teacher should recap the main points covered during the lesson, reinforcing the definition of Hess's Law, how it is applied to calculate enthalpy change, and the concept of enthalpy as a state function.
   • The skills developed by the students during the practical activities, such as the ability to balance chemical equations and apply Hess's Law to solve complex thermochemistry problems, should also be mentioned.

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

   • The teacher should explain how the lesson connected the theory of Hess's Law with practice, through modeling and problem-solving activities.
   • Practical applications of Hess's Law should also be reinforced, mentioning examples of its use in the chemical industry and everyday life.

3. Extra Study Materials: (1 - 2 minutes)

   • The teacher should suggest extra materials for students who want to deepen their knowledge of Hess's Law.
   • These materials can include chemistry books, educational websites, explanatory videos, and additional problems to solve.
   • The teacher should ensure that the suggested materials are appropriate for the students' level of understanding and that they are able to access them.

4. Importance of the Subject in Daily Life: (1 minute)

   • To conclude, the teacher should emphasize the importance of Hess's Law in daily life, explaining that it is present in many chemical processes that occur around us.
   • For example, the importance of Hess's Law in the food industry, fuel production, and understanding natural phenomena such as photosynthesis and respiration can be mentioned.
   • The teacher should reinforce that the study of thermochemistry and Hess's Law is not only relevant for understanding the world around us but also for developing analytical and problem-solving skills that are useful in many other areas of science and life.