Lesson Plan | Traditional Methodology | Electrochemistry: Nernst Equation

Objectives

Duration: 10 - 15 minutes

The purpose of this stage is to provide students with a clear understanding of the lesson's objectives. By describing what will be learned and highlighting the necessary skills, students will be better prepared to absorb the content and understand the practical application of the Nernst equation. This establishes a solid foundation for subsequent learning and ensures that students know exactly what is expected of them.

Main Objectives

1. Explain the Nernst equation and its components.

2. Demonstrate how to use the Nernst equation to calculate the potential difference of a cell under non-standard conditions.

3. Provide practical and guided examples to facilitate students' understanding of the application of the Nernst equation.

Introduction

Duration: 10 - 15 minutes

The purpose of this stage is to capture students' attention and contextualize the importance of studying the Nernst equation. By providing an overview and interesting facts about the topic, students can perceive the practical relevance of the content, increasing their interest and motivation to learn.

Context

Electrochemistry is a branch of chemistry that studies the relationship between electricity and chemical reactions. One of the most important concepts in this field is the Nernst equation, which allows us to calculate the potential difference of an electrochemical cell under non-standard conditions. This concept is fundamental to understanding how batteries and cells used in our daily life work, such as those that power our cell phones and laptops.

Curiosities

Did you know that the principle of the Nernst equation is used in pH sensors, which are essential in various fields, from the food industry to water treatment? These sensors help ensure that the pH of solutions is within a safe and effective range, allowing for the control of chemical and biological processes.

Development

Duration: 50 - 60 minutes

The purpose of this stage is to provide a detailed and practical understanding of the Nernst equation, allowing students to apply theoretical knowledge to real calculations. By addressing specific components and solving practical problems, students can consolidate their understanding and develop the necessary skills to use the Nernst equation in various contexts. The proposed questions will reinforce learning and ensure that students can apply the equation independently.

Covered Topics

1. Introduction to the Nernst Equation 2. Explain what the Nernst equation is, highlighting that it allows for the calculation of the electrode potential under non-standard conditions. The equation is given by: E = E° - (RT/nF) * ln(Q), where E is the electrode potential, E° is the standard electrode potential, R is the universal gas constant, T is the temperature in Kelvin, n is the number of electrons involved in the reaction, F is Faraday's constant, and Q is the reaction quotient. 3. Components of the Nernst Equation 4. Detail each component of the Nernst equation: the gas constant (R = 8.314 J/(mol·K)), Faraday's constant (F = 96485 C/mol), the temperature (T) and how it should be converted to Kelvin, and the number of electrons (n) transferred in the redox reaction. Explain the reaction quotient (Q) and how it is calculated from the concentrations of the reactants and products. 5. Application of the Nernst Equation 6. Demonstrate how to apply the Nernst equation in practical calculations. Use specific examples, such as calculating the potential of a galvanic cell with different ion concentrations. Show step by step how to insert values into the equation and solve. 7. Practical Examples 8. Provide guided examples with different scenarios. For example, calculate the potential of a Daniell cell under the following conditions: [Zn^2+] = 0.1 M and [Cu^2+] = 0.01 M. Demonstrate how each component of the equation is determined and how the calculation is performed. 9. Importance and Applications of the Nernst Equation 10. Discuss the relevance of the Nernst equation in practical contexts, such as in pH sensors, batteries, and fuel cells. Highlight how the equation is fundamental for understanding and developing electrochemical technologies.

Classroom Questions

1. 1. Calculate the potential of a galvanic cell where the reaction is Zn(s) + Cu^2+(aq) -> Zn^2+(aq) + Cu(s), given the standard potentials E°(Zn^2+/Zn) = -0.76 V and E°(Cu^2+/Cu) = +0.34 V, under conditions: [Zn^2+] = 0.5 M and [Cu^2+] = 0.01 M at 25°C. 2. 2. An electrochemical cell has the reaction: Ag^+(aq) + Cl^-(aq) -> AgCl(s), with E°(Ag^+/Ag) = +0.80 V and E°(Cl^-/Cl2) = +1.36 V. Calculate the cell potential when [Ag^+] = 0.01 M and [Cl^-] = 0.1 M at 25°C. 3. 3. Determine the potential of a cell composed of the following half-reactions: Fe^3+(aq) + e^- -> Fe^2+(aq) with E° = +0.77 V and Cr^3+(aq) + 3e^- -> Cr(s) with E° = -0.74 V. The concentrations are [Fe^3+] = 0.1 M, [Fe^2+] = 0.01 M, and [Cr^3+] = 0.01 M at 25°C.

Questions Discussion

Duration: 15 - 20 minutes

The purpose of this stage is to ensure that students have understood how to apply the Nernst equation practically and independently. The detailed discussion of the questions helps clarify doubts and consolidate understanding. The engagement questions aim to stimulate critical thinking and the application of knowledge in real contexts, promoting a deeper and more meaningful learning experience.

Discussion

• 1. Question 1: To calculate the potential of the galvanic cell, the Nernst equation is applied as follows:

Given: E°(Zn^2+/Zn) = -0.76 V and E°(Cu^2+/Cu) = +0.34 V. Overall Reaction: Zn(s) + Cu^2+(aq) -> Zn^2+(aq) + Cu(s). Standard cell potential (E°cell): E°(Cu^2+/Cu) - E°(Zn^2+/Zn) = 0.34 V - (-0.76 V) = 1.10 V. Q (reaction quotient): [Zn^2+]/[Cu^2+] = 0.5/0.01 = 50. Nernst equation: E = E° - (RT/nF) * ln(Q), with T = 298 K, R = 8.314 J/(mol·K), F = 96485 C/mol, n = 2. Calculation: E = 1.10 V - (8.314 * 298 / (2 * 96485)) * ln(50) ≈ 1.10 V - 0.0296 * 3.91 ≈ 0.99 V.

Thus, the cell potential is approximately 0.99 V.

• 2. Question 2: For the electrochemical cell with the reaction Ag^+(aq) + Cl^-(aq) -> AgCl(s):

Given: E°(Ag^+/Ag) = +0.80 V and E°(Cl^-/Cl2) = +1.36 V. Overall Reaction: Ag^+(aq) + Cl^-(aq) -> AgCl(s). Standard cell potential (E°cell): E°(Ag^+/Ag) - E°(Cl^-/Cl2) = 0.80 V - 1.36 V = -0.56 V. Q (reaction quotient): [Ag^+][Cl^-] = 0.01 * 0.1 = 0.001. Nernst equation: E = E° - (RT/nF) * ln(Q), with T = 298 K, R = 8.314 J/(mol·K), F = 96485 C/mol, n = 1. Calculation: E = -0.56 V - (8.314 * 298 / 96485) * ln(0.001) ≈ -0.56 V - 0.0257 * (-6.91) ≈ -0.56 V + 0.177 ≈ -0.38 V.

Thus, the cell potential is approximately -0.38 V.

• 3. Question 3: For the cell composed of the half-reactions:

Given: E°(Fe^3+/Fe^2+) = +0.77 V and E°(Cr^3+/Cr) = -0.74 V. Overall Reaction: 3Fe^2+(aq) + Cr^3+(aq) -> 3Fe^3+(aq) + Cr(s). Standard cell potential (E°cell): E°(Fe^3+/Fe^2+) - E°(Cr^3+/Cr) = 0.77 V - (-0.74 V) = 1.51 V. Q (reaction quotient): [Fe^3+]^3/[Fe^2+]^3[Cr^3+] = (0.1)^3 / (0.01)^3 * 0.01 = 10^3 / 10^-2 = 10^5. Nernst equation: E = E° - (RT/nF) * ln(Q), with T = 298 K, R = 8.314 J/(mol·K), F = 96485 C/mol, n = 3. Calculation: E = 1.51 V - (8.314 * 298 / (3 * 96485)) * ln(10^5) ≈ 1.51 V - 0.0257 * 11.51 ≈ 1.51 V - 0.29 ≈ 1.22 V.

Thus, the cell potential is approximately 1.22 V.

Student Engagement

1. What difficulties have you encountered in applying the Nernst equation? 2. How does temperature influence the results obtained from the Nernst equation? 3. In what other practical situations do you think the Nernst equation can be applied? 4. Why is it important to consider the concentrations of reactants and products in the Nernst equation? 5. Discuss how the Nernst equation can be applied in modern technologies such as lithium batteries and sensors.

Conclusion

Duration: 10 - 15 minutes

The purpose of this stage is to recap the main points covered in the lesson, reinforcing students' learning. By reviewing the content and connecting theory with practice, students consolidate their understanding and recognize the relevance of the studied topic. This stage also serves to clarify any remaining doubts and conclude the lesson cohesively.

Summary

• The Nernst equation allows calculating the electrode potential under non-standard conditions.
• Components of the Nernst equation: E, E°, R, T, n, F, and Q.
• How to calculate the reaction quotient (Q) from the concentrations of reactants and products.
• Application of the Nernst equation in practical calculations with specific examples.
• Importance of the Nernst equation in pH sensors, batteries, and fuel cells.

The lesson connected theory with practice by demonstrating how the Nernst equation is used to calculate the electrode potential under non-standard conditions, providing practical and guided examples that illustrated the application of theory in real situations, such as determining the potential of galvanic cells with different ion concentrations.

The Nernst equation is fundamental for understanding the electrochemical reactions that occur in common devices such as batteries and pH sensors. These devices are essential in our daily lives, from powering our electronic devices to monitoring water quality. Understanding this equation helps to comprehend and improve these technologies.