Contextualization
Chemistry is a science concerned with understanding the transformation of matter, and one of its fundamental aspects is the study of chemical reactions that occur in the universe. In this context, enthalpy emerges as a measure of heat involved in such reactions.
The enthalpy, represented by the letter H, is a thermodynamic state function that is closely related to the concept of internal energy. It considers the total energy of a system, including kinetic energy, potential energy, and volume of the system. In chemical reactions, the enthalpy difference between reactants and products (ΔH) is valuable information, as it indicates the amount of energy that will be released or absorbed during the reaction, allowing us to classify them as exothermic (release energy, ΔH is negative) or endothermic (absorb energy, ΔH is positive).
For example, when we light a match, an exothermic process occurs, in which the energy initially contained in the reactants (phosphorus and oxygen from the air) is released as heat (and light), making the final enthalpy less than the initial one. Thus, enthalpy is a direct measure of the 'amount of fire' a reaction can produce.
Enthalpy manifests itself in various forms around us; the importance of understanding it is reflected in several areas, including industry, medicine, cooking, and more. In the case of the refrigeration industry, for example, enthalpy is vital to understanding the refrigeration process, since by absorbing heat from the environment (endothermic process), the refrigerant vaporizes, cooling the surrounding environment. In a more everyday scenario, enthalpy is also responsible for the hot air we feel when we open a pressure cooker, an exothermic process.
References for further exploration of the topic:
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“Physical Chemistry” by Peter Atkins and Julio de Paula. 9th Edition. Link
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YouTube video “Enthalpy - Energy of Chemical Reactions”. Manual do Mundo channel. Link
Hands-on activity: Understanding enthalpy through the burning of food
Project Objective
The objective of this project is to understand and calculate the enthalpy of chemical reactions through a hands-on activity: the burning of food. Students will measure the amount of heat released in the combustion (burning) of different foods, in order to estimate the energy (in calories) that they would provide if consumed.
Detailed project description
Students will be divided into groups of 3 to 5 people. They will conduct an experiment to understand the enthalpy concept of reactions, using food as reactants. The experiment will explore the concept of exothermic reactions, where energy is released, and will allow students to compare the energy (heat) values released by burning different foods.
The activity will be developed in three stages: experiment preparation, execution, and analysis of results. After performing the experiment, the groups will consolidate the obtained results in a report, which should be submitted within a month. Each student is expected to dedicate between 5 and 10 hours to complete this project.
Materials needed
- Common foods (such as popcorn, peanuts, chips, etc.).
- A calorimeter (can be an aluminum can with water).
- A scale.
- A thermometer.
- Tongs.
- Matches.
Step-by-step
- Stage 1: Experiment preparation
Students should conduct a literature review on enthalpy from books and reliable websites. This will help them understand the concept of enthalpy and prepare for the hands-on experiment.
- Stage 2: Experiment Execution
Students should measure the mass of each food before burning it. They should then burn each food under the calorimeter with water, recording the temperature change of the water caused by the heat from the burning food. This will allow them to calculate the amount of energy (heat) that was released in the combustion reaction.
- Stage 3: Analysis of Results
Students will use the collected data (mass of food and temperature change of water) to calculate the amount of energy released per gram of each food, representing the enthalpy of the food's combustion chemical reaction.
Project Deliverables
At the end of the experiment, each group should submit a report in a document format containing:
1. Introduction: Contextualization of the theme, relevance and application to the real world, purpose of the project.
2. Development: Explanation of the theory behind the key concept of enthalpy, detailed description of the activity, methodology used, and presentation and discussion of the obtained results. Students should show how the calculations were performed, and what the obtained value means in terms of enthalpy and heat released. Projects that address the importance and implications of these results for everyday life will be evaluated more positively.
3. Conclusion: Summary of the main points of the report, reflections on what was learned, and conclusions drawn from the project.
4. Bibliography: Sources consulted for the development of the project.
Remember that the report should be clear, well-written, and represent a team effort. Additionally, the experiment should be carried out safely, without putting the students at risk.
