Lesson plan of Thermochemistry: Gibbs Free Energy

Objectives (5 - 7 minutes)

1. Understand the concept of Gibbs Free Energy and its importance in chemical thermodynamics.
2. Apply the mathematical formula of Gibbs Free Energy to calculate whether a reaction is spontaneous or not at a given temperature.
3. Analyze and interpret Gibbs Free Energy graphs as a function of time and temperature to predict the spontaneity of a reaction.

Secondary objectives:

• Stimulate logical-mathematical reasoning skills by applying the Gibbs Free Energy formula.
• Develop graphing interpretation and chemical reaction behavior prediction skills.
• Promote understanding of the importance of chemical thermodynamics in the study of chemical reactions.

Introduction (10 - 12 minutes)

1. Review of Previous Concepts:

   • The teacher begins the lesson by reviewing fundamental concepts for understanding chemical thermodynamics, such as enthalpy (ΔH), entropy (ΔS), and temperature (T). It is important to emphasize that these concepts are fundamental to understanding Gibbs Free Energy (ΔG).
   • The teacher may ask quick questions to students to check their understanding of these concepts and clarify any questions that may arise.

2. Introduction of Problem Situations:

   • The teacher presents two problem situations involving Gibbs Free Energy:
     1. Situation 1: A student has two reactions, one exothermic and one endothermic. He wants to know which is more spontaneous. How can he use Gibbs Free Energy to answer this question?
     2. Situation 2: Another student has the same question, but now he wants to know the temperature at which the two reactions become equally spontaneous. How can he use the Gibbs Free Energy formula to solve this question?

3. Importance of the Subject:

   • The teacher contextualizes the importance of Gibbs Free Energy, explaining that it is used to determine whether or not a reaction is spontaneous and, therefore, whether or not it will occur. This is crucial information in many areas of chemistry, such as the pharmaceutical industry, where it is necessary to control and optimize chemical reactions.

4. Introduction of the Topic:

   • The teacher introduces the topic of the lesson, explaining that Gibbs Free Energy is a thermodynamic function that combines enthalpy, entropy, and temperature. He can emphasize that Gibbs Free Energy is a fundamental quantity in chemistry and is often used to predict the spontaneity of a reaction.
   • The teacher may pique students' curiosity by mentioning that Gibbs Free Energy was formulated by Josiah Willard Gibbs, an American physicist and chemist who is considered one of the founders of chemical thermodynamics.

Development (20 - 25 minutes)

1. Theory: Concept of Gibbs Free Energy (7 - 10 minutes)

   • The teacher begins the theoretical part by explaining that the Gibbs Free Energy (ΔG) is a thermodynamic function that combines the enthalpy (ΔH), entropy (ΔS), and temperature (T) of a system. He can write the Gibbs Free Energy equation on the blackboard: ΔG = ΔH - TΔS.
   • Then, the teacher describes how Gibbs Free Energy is used to determine whether a reaction is spontaneous or not. He explains that if ΔG is negative, the reaction is spontaneous (i.e., it will occur without the need for an external energy source). If ΔG is positive, the reaction is non-spontaneous (i.e., it will not occur without an external energy source). And if ΔG is equal to zero, the reaction is in equilibrium.
   • The teacher can use practical examples to illustrate these concepts. For example, he can talk about the combustion reaction of methane, which has a negative ΔG and is therefore spontaneous. He can also talk about the formation reaction of methane, which has a positive ΔG and is therefore non-spontaneous.

2. Practical Examples of the Application of Gibbs Free Energy (7 - 10 minutes)

   • The teacher proposes two examples of the application of the Gibbs Free Energy formula to solve problems. He may use the problem situations presented in the Introduction as a starting point.
   • In the first example, the teacher asks the students to calculate the Gibbs Free Energy of two reactions, one exothermic and one endothermic, and to determine which of them is more spontaneous. The teacher guides students to find the values of ΔH and ΔS of the reactions in their thermochemical tables and substitute these values into the Gibbs Free Energy formula. He then explains how to interpret the value of ΔG to answer the question.
   • In the second example, the teacher asks the students to solve a slightly more complex problem: to determine the temperature at which the two reactions in the previous example become equally spontaneous. He guides the students to equate the ΔG expressions of the two reactions and solve the resulting equation for T. The teacher then explains how to interpret the value of T to answer the question.

3. Interpretation of Gibbs Free Energy Graphs (6 - 8 minutes)

   • The teacher introduces the concept of a Gibbs Free Energy graph as a function of time and temperature. He explains that these graphs are used to predict the spontaneity of a reaction at different temperatures.
   • The teacher draws a Gibbs Free Energy vs. time graph on the blackboard and explains how to interpret this graph. He emphasizes that if the curve of the graph is below the x-axis, the reaction is spontaneous. If the curve is above the x-axis, the reaction is non-spontaneous. And if the curve crosses the x-axis, the reaction is in equilibrium.
   • The teacher then draws a Gibbs Free Energy vs. temperature graph and explains how to interpret this graph. He emphasizes that the slope of the curve in the graph indicates whether the reaction is favored at high or low temperatures. If the curve is negative, the reaction is favored at high temperatures. If the curve is positive, the reaction is favored at low temperatures.
   • The teacher can use concrete examples to illustrate these concepts. For example, he can draw the Gibbs Free Energy graph of the methane combustion reaction and explain how to interpret this graph to predict the spontaneity of the reaction at different temperatures.

Return (8 - 10 minutes)

1. Recapitulation of Content (3 - 4 minutes)

   • The teacher begins the Return stage by briefly recapitulating the main content covered during the lesson. He reinforces the concepts of Gibbs Free Energy, its formula, and the interpretation of the ΔG values.
   • Then, the teacher recalls the practical examples solved during the lesson, highlighting how the Gibbs Free Energy formula was applied to solve the proposed problems.
   • The teacher can use the Socratic questioning technique, asking students questions and requesting that they recount the concepts and examples discussed. This helps to consolidate learning and identify possible gaps in understanding.

2. Connection between Practice and Theory (2 - 3 minutes)

   • The teacher proposes that the students reflect on how the theory presented in the lesson connects with practice. He can ask the students how they could use the concept of Gibbs Free Energy to understand and predict the spontaneity of reactions in everyday situations or in other disciplines.
   • The teacher can also highlight how the lesson connected the theory of chemical thermodynamics with the practice of solving problems and interpreting graphs. He can reinforce the importance of understanding the theory in order to be able to apply it in a practical and effective way.

3. Reflection on the Learning (3 - 4 minutes)

   • The teacher proposes that the students reflect on what they have learned during the lesson. He can ask questions such as: "What was the most important concept you learned today?" and "Which questions have not yet been answered?".
   • The teacher can also ask students to assess their own level of understanding of the topic, using a scale of 1 to 5. This can help to identify students who need reinforcement or extra attention in the next lesson.

4. Teacher Feedback (1 minute)

   • Finally, the teacher provides general feedback on the students' participation and performance during the lesson. He can praise the students' effort and dedication, and also highlight areas that need more attention or practice.
   • The teacher can also reinforce the importance of the topic of the lesson and encourage students to continue studying and practicing the concepts learned.

Conclusion (5 - 7 minutes)

1. Recapitulation of Content (2 - 3 minutes)

   • The teacher begins the Conclusion stage by recalling the main points covered during the lesson. He recapitulates the definition and formula of Gibbs Free Energy, as well as the interpretation of its values.
   • The teacher can do a quick review of the practical examples and the Gibbs Free Energy graphs, reinforcing the application of the theoretical concepts in problem solving.

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

   • The teacher emphasizes how the lesson connected the theory of Gibbs Free Energy with the practice of problem solving and with applications in the real world. He can recall how the theoretical concepts were applied in the practical examples and how the understanding of Gibbs Free Energy is fundamental to predicting the spontaneity of chemical reactions.
   • The teacher can mention some practical applications of Gibbs Free Energy, such as the optimization of chemical reactions in the pharmaceutical industry, the prediction of reactions in biological processes, and the understanding of natural phenomena such as combustion and photosynthesis.

3. Complementary Materials (1 - 2 minutes)

   • The teacher suggests some complementary study materials for students who wish to deepen their knowledge of Gibbs Free Energy. These materials may include Chemistry textbooks, online instructional videos, Chemistry education websites, and extra exercises.
   • The teacher can also indicate some practical activities that students can do to reinforce their understanding of the subject, such as solving more exercises, interpreting Gibbs Free Energy graphs, conducting simple experiments involving chemical reactions, among others.

4. Importance of the Subject (1 minute)

   • Finally, the teacher reinforces the importance of the subject presented for everyday life and for the students' education. He can emphasize that understanding Gibbs Free Energy is fundamental to understanding the spontaneity of chemical reactions, an essential concept in many areas of Chemistry.
   • The teacher can also point out that the study of Gibbs Free Energy develops important skills in students, such as logical-mathematical reasoning, graph interpretation, problem solving, and the application of theoretical concepts in practice. These skills are valuable not only in Chemistry, but in many other disciplines and situations in life.