Lesson Plan | Active Methodology | Thermochemistry: Hess's Law

Premises: This Active Lesson Plan assumes: a 100-minute class duration, prior student study both with the Book and the beginning of Project development, and that only one activity (among the three suggested) will be chosen to be carried out during the class, as each activity is designed to take up a large part of the available time.

Objective

Duration: (5 - 10 minutes)

The Objectives stage is crucial for setting the tone and focus of the lesson. By clearly outlining what students are expected to learn, the teacher helps prepare and engage them with the content. This step offers an overview of the key topics, laying the groundwork for a deeper understanding of Hess's Law and its real-world applications.

Objective Utama:

1. Enable students to understand and apply Hess's Law to calculate the change in enthalpy for chemical reactions using enthalpies of formation and those derived from other reactions.

2. Develop students' critical analysis and logical reasoning skills to tackle practical problems involving Hess's Law.

Objective Tambahan:

1. Encourage student engagement through discussions and idea exchanges during the lesson.

Introduction

Duration: (20 - 25 minutes)

The introduction aims to engage students with the content they've already studied, utilizing problem-situations that mimic real-life contexts and challenge them to apply their theoretical knowledge. By contextualizing the topic with practical and historical examples, it helps cement understanding and highlights the significance of Hess's Law, paving the way for practical classroom activities.

Problem-Based Situation

1. Imagine you're a chemist tasked with developing a new industrial process that requires the reaction of two compounds to obtain a desired product. However, the direct reaction is incredibly exothermic and poses safety risks. How could you utilize Hess's Law to determine if a safer alternative pathway, involving intermediate reactions, is achievable?

2. Picture yourself at a chemistry competition, challenged to calculate the enthalpy of formation for a compound that can't be directly measured in the lab. Use the enthalpies of formation of other compounds along with Hess's Law to resolve this issue.

Contextualization

Hess's Law is foundational not only in labs but also in industries where the safety and efficiency of chemical processes are paramount. Take, for example, the production of ammonia for fertilizers; the direct reaction of nitrogen and hydrogen is highly exothermic and risky. Hence, applying Hess's Law to compute the enthalpies of intermediate reactions is vital for ensuring a safe and effective process. Furthermore, understanding the history of Hess's Law, discovered by Germain Hess in the 19th century, highlights the evolution of scientific thought and the relevance of thermodynamics in modern chemistry.

Development

Duration: (75 - 85 minutes)

The Development phase in this flipped classroom approach encourages students to collaboratively and practically apply their knowledge of Hess's Law. By working in groups, they strengthen their theoretical understanding and develop skills in communication, collaboration, and critical thinking. The activities proposed are designed to be engaging and challenging, ensuring that students are deeply involved in addressing complex problems, equipping them for real-world scenarios, and sparking creativity.

Activity Suggestions

It is recommended that only one of the suggested activities be carried out

Activity 1 - The Chemists' Race: Unraveling Exothermic and Endothermic Reactions

> Duration: (60 - 70 minutes)

- Objective: Apply Hess's Law to calculate the enthalpy of chemical reactions, while fostering teamwork and quick problem-solving skills.

- Description: In this fun activity, students will be sorted into teams of up to 5, simulating a race among chemists to uncover the enthalpy of a reaction that can't be directly measured. They'll be provided with the enthalpies of formation for reactants and products, and will need to calculate both the enthalpy of the direct reaction and a proposed alternative route, applying Hess's Law. The challenge will be timed, and the first group to present the accurate and most efficient calculation will win.

- Instructions:

• Organize the class into groups of up to 5 students.

• Hand out the data on the enthalpies of formation for the reactants and products.

• Introduce the direct reaction and the proposed alternative route.

• Keep track of each group's time for calculations.

• Have each group present their findings and explain their application of Hess's Law.

• Announce the winner based on both accuracy and efficiency.

Activity 2 - The Mystery of the Missing Reactions

> Duration: (60 - 70 minutes)

- Objective: Enhance deduction skills and apply Hess's Law in intricate situations, encouraging teamwork and creativity among students.

- Description: In this group activity, students will receive a 'mystery box' containing cards representing the enthalpies of formation for various compounds and reactions. Some cards will be missing, symbolizing 'missing reactants.' Their task will be to piece together the missing reactions and calculate their enthalpies using Hess's Law. Each group will also have to create and present a 'crime theory' that explains the disappearance of the reactions based on their calculations.

- Instructions:

• Create a mystery box filled with enthalpy of formation cards.

• Assign one box to each group and explain the challenge.

• Allow groups to discuss and begin reconstructing the missing reactions.

• Provide support as they apply Hess's Law.

• Ask each group to present their 'crime theory' along with their calculations.

• Discuss the solutions as a class and clarify which reactions were genuinely missing.

Activity 3 - The Chemical Chef: Crafting the Perfect Reaction Recipe

> Duration: (60 - 70 minutes)

- Objective: Use Hess's Law to fine-tune chemical reactions, reinforcing understanding of stoichiometry and enthalpy, while promoting teamwork and innovation.

- Description: In this light-hearted scenario, each group of students will take on the role of 'chemical chefs' tasked with 'cooking' a chemical reaction. They'll receive 'ingredients' (enthalpies of formation) and an unfinished 'recipe.' The goal is to calculate the total enthalpy of the reaction, adjusting the amounts of 'ingredients' (stoichiometric coefficients) to ensure the reaction is thermally sustainable. The group that prepares the 'most balanced recipe,' generating the lowest enthalpy, will win.

- Instructions:

• Split students into groups and hand out the 'ingredients' and incomplete 'recipe.'

• Explain they need to compute and adjust the stoichiometric coefficients to minimize the final reaction enthalpy.

• Guide groups in applying Hess's Law to carry out the calculations.

• Invite each group to share their final 'recipe' and the calculations they performed.

• Evaluate the presentations and declare the group with the 'most balanced recipe' the winner.

Feedback

Duration: (10 - 15 minutes)

This Feedback stage is vital for consolidating student learning and ensuring they can reflect on how to apply the knowledge gained. Through group discussions, students have the opportunity to articulate their understanding, consider different viewpoints, and learn from peers' experiences. This also allows the teacher to gauge comprehension levels and clarify any outstanding questions, ensuring that the learning objectives have been met effectively.

Group Discussion

Kick off the group discussion by inviting each team to share their discoveries and the processes they undertook to reach them. Encourage students to explain how they applied Hess's Law during the different activities and what challenges they encountered. Use guiding questions to facilitate the sharing of ideas and ensure all key points are covered. The teacher should steer this discussion, acting as a moderator to ensure every student has a chance to contribute and that the discussions are productive and aligned with learning objectives.

Key Questions

1. What were the main challenges you faced while applying Hess's Law in the various activities?

2. How can understanding Hess's Law be useful in practical situations, like in industry or scientific breakthroughs?

3. Did you experience any surprises or discoveries during the activities that shifted your perspective on the topic?

Conclusion

Duration: (5 - 10 minutes)

The aim of the Conclusion is to solidify the knowledge acquired during the lesson, ensuring students can connect theoretical concepts with the practices they studied and applied. This moment also serves to highlight the importance of the topic at hand, relating it to practical, everyday applications, and motivating students to view chemistry as an engaging and essential science for their lives and future careers.

Summary

To wrap up, the teacher should recap the key points regarding Hess's Law, highlighting students' ability to utilize enthalpies of formation and intermediate reactions to determine the enthalpy of any reaction. It's important to underscore that enthalpy is a property of a system that can be quantified, and that Hess's Law plays a crucial role in calculating enthalpies in reactions that aren't directly observable.

Theory Connection

Today's lesson was designed to connect theory with practice in a cohesive manner. Students had the chance to directly apply the theoretical principles of Hess's Law through hands-on activities that mimic real-life scenarios and challenge their logical reasoning and math skills. This approach not only aids comprehension but also prepares students to apply their knowledge in real-world contexts, such as in industry or scientific research.

Closing

Finally, the teacher should emphasize the importance of Hess's Law in daily life and industry. Understanding the enthalpy of chemical reactions is crucial for the development of safe and efficient processes, like those in fertilizer and fuel production, where precise control of thermodynamic conditions is essential. Moreover, having the ability to accurately calculate enthalpies can pave the way for meaningful innovations and discoveries in chemistry and chemical engineering.