Exploring Internal Energy in Thermochemistry: Theory and Practice

Objectives

1. Understand that internal energy is the total energy stored by the particles of a system due to their movements and interactions.

2. Calculate internal energy under certain circumstances, using concepts from Thermochemistry.

3. Relate the concepts of internal energy to practical applications in the job market, such as in the chemical industry and engineering processes.

Contextualization

Imagine a moving car: it moves thanks to the energy stored in its fuel. Similarly, all substances store energy in their particles, known as internal energy. This energy is crucial for understanding chemical reactions and industrial processes, as it directly influences how and when transformations occur. For example, in food production, controlling internal energy during pasteurization ensures the safety and quality of the products. In engineering, optimizing internal energy in chemical reactions can increase efficiency and reduce production costs.

Relevance of the Theme

Internal energy is a vital concept in areas such as chemical engineering and the food industry. Understanding how energy is stored and distributed in a system is essential for various practical applications, especially in industrial contexts where efficient energy management is crucial. Developing practical skills and connecting theoretical concepts with the real world prepares students to face challenges in the job market.

Internal Energy

Internal energy is the total energy stored by the particles of a system due to their movements and interactions. This energy includes both kinetic energy, which is generated by the movement of particles, and potential energy, which results from their interactions. Understanding internal energy is fundamental for analyzing thermodynamic systems and optimizing industrial processes.

• Internal energy is the sum of the kinetic and potential energies of all the particles in a system.

• It is a state function, meaning it depends only on the current state of the system and not on the path taken to reach that state.

• Changes in internal energy can occur through heat transfer or work done.

Factors that Influence Internal Energy

There are several factors that can influence the internal energy of a system, including temperature, amount of substance, pressure, and volume. These factors determine how energy is distributed among the particles of the system and how it can be altered through thermodynamic processes.

• Temperature is directly proportional to the average kinetic energy of the particles.

• The amount of substance (number of moles) affects the total energy stored in the system.

• The pressure and volume of the system can alter the potential energy of the particles.

Methods for Calculating Internal Energy

Methods for calculating internal energy often involve using the first law of thermodynamics, which establishes energy conservation. The change in internal energy can be calculated by considering the amount of heat transferred to the system and the work done by the system.

• The first law of thermodynamics is expressed by the equation ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat transferred, and W is the work done.

• For closed systems, the change in internal energy can be calculated without considering mass exchange with the environment.

• Specific heat and heat capacity are important parameters for determining the amount of heat needed to change the internal energy.

Practical Applications

• In the chemical industry, controlling internal energy is crucial for the safety and efficiency of chemical reactions. For example, in the production of ammonia through the Haber-Bosch process, controlling temperature and pressure is essential for optimizing production.
• In the food industry, the pasteurization of dairy products involves controlling internal energy to ensure the elimination of pathogenic microorganisms without compromising product quality.
• In heating and cooling systems, such as air conditioners, internal energy calculations are used to size the equipment capacity and ensure thermal comfort with energy efficiency.

Key Terms

• Internal Energy: Total energy stored by the particles of a system due to their movements and interactions.

• First Law of Thermodynamics: Principle of energy conservation that states that the change in internal energy of a system is equal to the difference between the heat added to the system and the work done by the system.

• Specific Heat: Amount of heat needed to raise the temperature of a unit mass of a substance by one degree Celsius.

• Heat Capacity: Amount of heat required to raise the temperature of a sample of substance by one degree Celsius.

Questions

• How can understanding internal energy contribute to improving energy efficiency in industrial processes?

• In what way is controlling internal energy important for safety and quality in food production?

• What challenges did you face when trying to calculate the change in internal energy in a closed system during the practical class? How did you overcome these challenges?

Conclusion

To Reflect

Throughout this lesson, we explored the concept of internal energy, understanding how it is stored and distributed among the particles of a system. We saw that this energy is crucial for various industrial processes, such as the pasteurization of food and the production of ammonia. Understanding internal energy allows us to optimize processes, improve energy efficiency, and reduce costs, while also ensuring the safety and quality of products. The practical experience conducted in class illustrated concretely how internal energy can be transformed and distributed in a closed system, connecting theoretical concepts with real-world applications. Reflecting on these aspects better prepares us to face challenges in the job market and apply knowledge practically and efficiently.

Mini Challenge - Practical Challenge: Exploring the Variation of Internal Energy

This mini-challenge aims to consolidate understanding of the variation of internal energy in a closed system through a practical activity.

• Form groups of 4 to 5 people.
• Use an empty PET bottle, balloons, hot water, a thermometer, adhesive tape, and a small candle.
• Fill the PET bottle halfway with hot water and seal it with the balloon.
• Observe and record the temperature of the water and the balloon over time.
• Light the candle and place it under the bottle (with care and supervision).
• Record the changes in temperature and the volume of the balloon.
• Discuss as a group how internal energy is being transformed and distributed in the system.