Lesson Plan | Lesson Plan Tradisional | Thermochemistry: Hess's Law

Objectives

Duration: (10 - 15 minutes)

This part of the lesson plan focuses on introducing students to Hess's Law, a crucial concept in Thermochemistry, and illustrating how it can be used to determine the enthalpy of chemical reactions. By clearly outlining the objectives, students will grasp what is expected of them and how to practically apply this knowledge.

Objectives Utama:

1. Clarify Hess's Law and its application in Thermochemistry.

2. Show how to use Hess's Law to determine the enthalpy of chemical reactions.

Introduction

Duration: (10 - 15 minutes)

This segment aims to introduce the lesson topic engagingly and informatively, providing students with a clear understanding of the significance of Thermochemistry and Hess's Law. By sharing interesting facts and practical applications, the goal is to captivate students’ attention and encourage their desire to learn the content.

Did you know?

Hess's Law is commonly employed in the chemical industry to compute the energy needed to produce chemical compounds on a large scale. For example, when synthesizing ammonia (NH₃) using the Haber-Bosch process, Hess's Law is instrumental in optimizing production conditions, which can lead to significant energy and cost savings. Moreover, this law is also relevant in fuel studies and developing more efficient energy storage materials.

Contextualization

At the beginning of the lesson on Hess's Law, it's essential to provide students with context about the overall concept of Thermochemistry. Discuss that Thermochemistry is a branch of Chemistry that examines the energy changes, mainly as heat, that occur during chemical reactions. Stress that identifying the amount of energy involved in these reactions is one of Chemistry's key challenges, which is vital for various industrial and scientific uses.

Concepts

Duration: (40 - 50 minutes)

This part of the lesson plan aims to enhance students' understanding of Hess's Law by providing an in-depth presentation of the concepts and practicing problem-solving skills. By covering crucial topics and offering practical examples, the teacher guarantees that students comprehend how to apply Hess's Law in determining the enthalpy of chemical reactions, thereby nurturing their analytical and problem-solving capabilities in Thermochemistry.

Relevant Topics

1. Definition of Hess's Law: Clarify that Hess's Law indicates that the enthalpy change for a chemical reaction is consistent, regardless of the path taken, provided the initial and final conditions are the same. Emphasize that this law stems directly from the first law of thermodynamics.

2. Enthalpy of Formation: Explain that the enthalpy of formation refers to the heat change when one mole of a compound forms from its constituent elements in their standard states. Offer examples of enthalpy of formation tables and their application in calculations.

3. Application of Hess's Law: Illustrate how to utilize Hess's Law to compute the enthalpy of a reaction. Present examples of reactions where enthalpy can be derived by summing the enthalpies of intermediate reactions. Provide a step-by-step approach, demonstrating how to rearrange and combine chemical equations to achieve the desired value.

4. Calculation Example: Offer a detailed calculation example employing Hess's Law. For instance, compute the enthalpy of formation for the combustion of methane (CH₄). Supply all steps involved, from selecting intermediate reactions to aggregating the enthalpies of formation.

5. Problem Solving: Present additional problems and work through them with the students, emphasizing key steps and common mistakes. Ensure students comprehend how to independently apply Hess's Law.

To Reinforce Learning

1. Calculate the enthalpy change for the reaction: N₂(g) + 3H₂(g) → 2NH₃(g) using the following intermediate reactions: N₂(g) + O₂(g) → 2NO(g) ΔH = +180.5 kJ 2NO(g) + O₂(g) → 2NO₂(g) ΔH = -113.1 kJ 4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g) ΔH = -1170 kJ 2H₂(g) + O₂(g) → 2H₂O(g) ΔH = -571.6 kJ

2. Use Hess's Law to find the enthalpy of formation of CO₂(g) from the following reactions: C(s) + O₂(g) → CO₂(g) ΔH = -393.5 kJ CO(g) + 1/2O₂(g) → CO₂(g) ΔH = -283 kJ C(s) + 1/2O₂(g) → CO(g) ΔH = -110.5 kJ

3. Given the reaction: 2SO₂(g) + O₂(g) → 2SO₃(g) ΔH = -198 kJ, determine the enthalpy of formation of SO₃(g) using these reactions: S(s) + O₂(g) → SO₂(g) ΔH = -296.8 kJ

Feedback

Duration: (20 - 25 minutes)

This segment aims to review the solutions to the questions posed during the development phase of the lesson, ensuring that students grasp the methods and rationale employed in practical applications of Hess's Law. Additionally, it fosters student engagement, allowing them to share their solutions and concerns, which enriches collective learning.

Diskusi Concepts

1. Explain the enthalpy change for the reaction: N₂(g) + 3H₂(g) → 2NH₃(g): Reaction 1: N₂(g) + O₂(g) → 2NO(g) ΔH = +180.5 kJ Reaction 2: 2NO(g) + O₂(g) → 2NO₂(g) ΔH = -113.1 kJ Reaction 3: 4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g) ΔH = -1170 kJ Reaction 4: 2H₂(g) + O₂(g) → 2H₂O(g) ΔH = -571.6 kJ To solve, rearrange the intermediate reactions so that their sum equals the target reaction. Confirm that the summation of the intermediate enthalpies provides the enthalpy change of the target reaction. 2. Use Hess's Law to find the enthalpy of formation of CO₂(g): Reaction 1: C(s) + O₂(g) → CO₂(g) ΔH = -393.5 kJ Reaction 2: CO(g) + 1/2O₂(g) → CO₂(g) ΔH = -283 kJ Reaction 3: C(s) + 1/2O₂(g) → CO(g) ΔH = -110.5 kJ Rearrange the reactions and add the enthalpy changes to find the desired enthalpy of formation. 3. Determine the enthalpy of formation of SO₃(g): Reaction 1: S(s) + O₂(g) → SO₂(g) ΔH = -296.8 kJ Reaction 2: 2SO₂(g) + O₂(g) → 2SO₃(g) ΔH = -198 kJ Divide Reaction 2 by 2 and add it to Reaction 1 to derive the enthalpy of formation of SO₃(g).

Engaging Students

1. How is Hess's Law applied in industrial processes? 2. What challenges arise when using Hess's Law to compute enthalpy in complex reactions? 3. Why is it crucial to understand the enthalpies of formation of compounds? 4. How does Hess's Law correlate with the first law of thermodynamics? 5. Encourage students to describe, in their own words, how they adjusted and summed the intermediate reactions to derive the required enthalpy changes.

Conclusion

Duration: (10 - 15 minutes)

This part of the lesson aims to summarize the essential points discussed throughout the lesson, reinforcing students' comprehension. Moreover, it seeks to link theoretical knowledge to practical applications and underscore the relevance of the content to real-life situations, consolidating what has been learned and inspiring students to apply it in the real world.

Summary

['Thermochemistry studies energy exchanges, primarily in the form of heat, that occur during chemical reactions.', "Hess's Law states that the enthalpy change of a reaction is constant, regardless of the path taken, provided the initial and final states remain unchanged.", 'The enthalpy of formation signifies the enthalpy change when one mole of a compound is created from its elements in their standard states.', "Hess's Law can be utilized to calculate the enthalpy of a reaction by adding the enthalpies of intermediate reactions.", "Practical calculation examples employing Hess's Law have been provided and solved."]

Connection

The lesson linked the theory of Hess's Law with its application by showcasing detailed examples of enthalpy calculations and collaboratively solving problems with students. This illustrated how the law can be put to use in real-world situations, such as the synthesis of chemical compounds and applications in the fuel industry.

Theme Relevance

Hess's Law is key in understanding the energy repercussions of chemical reactions, significantly impacting various sectors including industrial compound production, advanced materials development, and energy process studies. For instance, optimizing ammonia production or creating more efficient fuels are direct, practical implications of this knowledge.