Lesson Plan | Traditional Methodology | Thermodynamics: 1st Law of Thermodynamics

Objectives

Duration: (10 - 15 minutes)

The purpose of this stage is to present the central points that will be addressed during the class to the students, providing a clear and objective overview of the skills they should acquire by the end of the meeting. This will help to guide the focus of learning and prepare students for the concepts and calculations that will be detailed later.

Main Objectives

1. Understand that energy can be transformed, but not created or destroyed, according to the first law of thermodynamics.

2. Learn to calculate work, change in internal energy, and heat exchanged, using the first law of thermodynamics.

3. Identify practical situations where the first law of thermodynamics is applied.

Introduction

Duration: (10 - 15 minutes)

The purpose of this stage is to engage students with the topic, showing the relevance and practical applications of the First Law of Thermodynamics. This will help to spark students' interest and curiosity, preparing them for a deeper understanding of the concepts that will be covered throughout the class.

Context

To start the class on the First Law of Thermodynamics, begin by highlighting the importance of energy in our daily lives. Explain that energy is present in various forms around us, whether in the light that illuminates the room, the warmth of the sun, or the electrical energy that powers our devices. The First Law of Thermodynamics, also known as the Principle of Conservation of Energy, is one of the fundamental laws of Physics that helps us understand how energy is transformed from one form to another without being created or destroyed.

Curiosities

Did you know that the First Law of Thermodynamics is applied in various fields, such as motor engineering and meteorology? For example, car engines use this law to convert the chemical energy of fuel into mechanical energy. In addition, it is essential for understanding climatic processes, such as storm formation and atmospheric circulation.

Development

Duration: (40 - 50 minutes)

The purpose of this stage is to deepen students' knowledge of the First Law of Thermodynamics, providing a solid foundation on the concepts of internal energy, work, and heat. In addition, by solving practical questions, students will be able to apply the theory learned and develop essential calculation skills for understanding thermodynamics.

Covered Topics

1. Concept of Internal Energy: Explain that the internal energy of a system is the sum of the kinetic and potential energies of the particles that make up the system. Highlight that this energy can be altered through work or heat transfer. 2. First Law of Thermodynamics: Present the mathematical formula of the first law of thermodynamics: ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat exchanged with the environment, and W is the work done by the system. Explain each term of the equation and how they relate to each other. 3. Work in Thermodynamic Processes: Detail how work can be calculated in different thermodynamic processes, such as isobaric, isochoric, isothermal, and adiabatic. Use P-V (pressure versus volume) graphs to illustrate each process and how work is represented by the area under the curve. 4. Heat Transfer: Explain the modes of heat transfer: conduction, convection, and radiation. Highlight practical examples of each mode and how they influence the internal energy of a system. 5. Practical Examples: Provide practical examples of the application of the first law of thermodynamics, such as in car engines, refrigerators, and biological processes. Use schematics and diagrams to illustrate these examples and facilitate student understanding.

Classroom Questions

1. 1. An ideal gas undergoes an isobaric expansion, doing 500 J of work. During this process, the gas absorbs 300 J of heat. What is the change in internal energy of the gas? 2. 2. Calculate the work done by an ideal gas that expands isothermally from 2.0 L to 4.0 L under a constant pressure of 1.0 atm. (Hint: 1 atm = 101.3 J/L) 3. 3. In an adiabatic process, an ideal gas undergoes compression and its internal energy increases by 200 J. What is the amount of heat exchanged with the environment during this process?

Questions Discussion

Duration: (20 - 25 minutes)

The purpose of this stage is to review and consolidate students' knowledge by discussing the answers to the presented questions and promoting a deeper understanding of the concepts covered. The discussion and reflection on the answers help students identify and correct possible comprehension errors, in addition to strengthening the practical application of the theory learned.

Discussion

• Question 1: An ideal gas undergoes an isobaric expansion, doing 500 J of work. During this process, the gas absorbs 300 J of heat. What is the change in internal energy of the gas?

To solve this question, use the first law of thermodynamics: ΔU = Q - W. Here, Q = 300 J and W = 500 J. Therefore, ΔU = 300 J - 500 J = -200 J. The change in internal energy of the gas is -200 J, indicating that the internal energy of the gas has decreased.

• Question 2: Calculate the work done by an ideal gas that expands isothermally from 2.0 L to 4.0 L under a constant pressure of 1.0 atm. (Hint: 1 atm = 101.3 J/L)

For an isothermal process, the work done, W, is given by W = P * ΔV. Here, P = 1.0 atm and ΔV = 4.0 L - 2.0 L = 2.0 L. Converting the pressure to joules, we have 1.0 atm = 101.3 J/L. Thus, W = 101.3 J/L * 2.0 L = 202.6 J.

• Question 3: In an adiabatic process, an ideal gas undergoes compression and its internal energy increases by 200 J. What is the amount of heat exchanged with the environment during this process?

For an adiabatic process, the amount of heat exchanged with the environment (Q) is zero. Therefore, any change in internal energy (ΔU) is equal to the work done (W). Here, ΔU = 200 J and, since Q = 0, we have ΔU = -W. Thus, W = -200 J, indicating that work was done on the gas.

Student Engagement

1. How does the first law of thermodynamics apply in everyday life? Give specific examples. 2. Why can the internal energy of a system be increased or decreased? What factors influence this variation? 3. What is the difference between an isobaric, isothermal, and adiabatic process? Explain with practical examples. 4. How can you relate the first law of thermodynamics to the efficiency of a car engine? 5. Discuss the importance of energy conservation in biological processes, such as cellular respiration.

Conclusion

Duration: (10 - 15 minutes)

The purpose of this stage is to provide a clear and concise summary of the main points addressed in the class, reinforcing the connection between theoretical concepts and their practical applications. In addition, it highlights the importance of the topic for students’ daily lives, consolidating learning and encouraging continuous curiosity about the subject.

Summary

• Energy cannot be created or destroyed, only transformed.
• The First Law of Thermodynamics is expressed by the equation ΔU = Q - W.
• Internal energy is the sum of the kinetic and potential energies of the particles in a system.
• Work and heat are means of transferring energy to or from a system.
• There are different thermodynamic processes: isobaric, isochoric, isothermal, and adiabatic.

The class connected theory and practice by demonstrating how the First Law of Thermodynamics applies in everyday situations, such as the functioning of car engines and biological processes. Practical examples and problem-solving helped students visualize how energy is transformed and transferred in different contexts.

The First Law of Thermodynamics is fundamental for understanding many phenomena around us. From the efficiency of vehicle engines to biological processes such as cellular respiration, understanding how energy is conserved and transformed is crucial. This law also helps us develop more efficient and sustainable technologies.