Contextualization

Enthalpy is a physical quantity that plays a crucial role in thermodynamics, the branch of physics that studies energy transformations. It is defined as the total amount of energy in a thermodynamic system. The enthalpy of a chemical reaction is the difference between the enthalpies of the reactants and products. It is an important quantity because it allows us to predict whether a reaction is exothermic (releasing energy) or endothermic (absorbing energy).

Determining reaction enthalpies is fundamental in chemistry, as it allows us to predict not only if a reaction is possible, but also the amount of energy involved in the reaction. This energy can be utilized (in the case of exothermic reactions) or needs to be supplied (in the case of endothermic reactions) for the reaction to occur. Understanding and being able to predict reaction enthalpy is therefore an essential tool for chemistry.

The calculation of enthalpy plays a crucial role in the world around us. It is present, for example, in determining the efficiency of fuels in cars or power plants, in evaluating the feasibility of industrial chemical processes, and even in our diet - our body obtains energy from the breakdown of food, which can be thought of as a set of chemical reactions whose enthalpies we need to understand.

As we become increasingly aware of the need for energy conservation and reduction of carbon emissions, understanding enthalpy and its role in thermodynamics becomes more and more relevant. In particular, green chemistry, which aims to develop more efficient and less environmentally harmful chemical processes, heavily relies on the understanding of thermodynamics and enthalpy.

Students can delve deeper into the topic through the following resources:

1. Book: Atkins, P., de Paula, J., & Frías, M. (2012). Principles of Chemistry: Questioning the Modern World and the Environment. 5th ed. Bookman Editora. (Chapter 3, The First Law of Thermodynamics).
2. Video: 'Thermodynamics and Enthalpy: What is Enthalpy?' Available on YouTube through the channel Ciência em Ação.
3. Website: Brasil Escola. 'Calculation of enthalpy variation'. Available at: https://brasilescola.uol.com.br/quimica/calculo-da-variacao-entalpia.htm

Practical Activity

Title: 'Study of Calorimetry and Calculation of Enthalpy in Chemical Reactions'

Project Objective

The main objective of the project is to provide simulation and practical experiments for calculating the enthalpy of chemical reactions. Students should understand the theory behind enthalpy calculation and apply it in practice using a calorimetry experiment. Additionally, they will also work on skills such as teamwork, time management, and problem-solving.

Project Description

Students will be divided into groups of 3 to 5 students. They will have one week to complete the project and should spend between two to four hours (per participant) to complete it.

Required Materials:

• A calorimeter (can be made with household materials like two aluminum cans, one larger than the other, and a thermometer to measure temperature changes.
• Reagents for the chosen chemical reaction (can be the dissolution of a known quantity of a salt, such as sodium chloride in water).
• Scale to measure the masses of the reagents.
• Stopwatch.
• Calculator.

Step by Step:

1. Preparation: Students should prepare the experiment, considering safety and precautions. They should assemble the calorimeter and correctly weigh the reagents to be used.
2. Experiment Execution: Students should record the initial temperature of the water (or other medium) in the calorimeter. Then, they should add the reagent and note the final temperature after the reaction. The start and end times of the reaction should be observed and recorded.
3. Calculations: Students should perform the necessary calculations to determine the enthalpy of the reaction, considering temperature changes and the amount of reacting substance.

Written Document:

After completing the experiment, each group should submit a report covering the following topics:

1. Introduction: The report should start with a brief introduction about what enthalpy is and why it is important in the context of chemistry. It should explain the project's objective and the expectations for its completion.

2. Development: In this section, students should detail step by step how they conducted the experiment, illustrating with photos or drawings if possible. They should also explain the theory behind the calculations performed, present the calculations, and discuss the results obtained.

3. Conclusion: In the conclusion, students should recap the main points, describe what they learned from the project, and draw conclusions based on their experiments and calculations.

4. References Used: Indicate the research and study sources used for the project.