Contextualization

Enthalpy is a physical quantity that allows us to understand the heat involved in a process at constant pressure. It is widely used in chemical reactions, especially in those that release or absorb energy, the so-called exothermic and endothermic processes. Essentially, enthalpy helps explain why certain reactions occur and others do not, even if the reactants are seemingly available.

The enthalpy of formation is an extremely relevant concept in chemistry, as it allows calculating the enthalpy of any chemical reaction from the enthalpies of formation of the reactants and products. For example, in combustion, a type of chemical reaction, enthalpy helps understand the amount of energy released in the form of heat. This has direct implications in our daily lives, from the simple act of lighting a match to the reactions that occur in a car engine.

To better understand these concepts, there is nothing better than getting hands-on. You, students, will have the opportunity to calculate the enthalpy of chemical reactions, understand how it works in practice, and, in addition, develop important skills such as time management, communication, and problem-solving.

Theoretical Introduction

Enthalpy (H) is a state function, meaning its value depends solely on the initial and final state of the system, regardless of the path taken. It is defined as the sum of the internal energy of a system (U) with the product of pressure (P) by its volume (V): H = U + PV.

The enthalpy of formation (ΔHf) is the energy change that occurs when 1 mole of a compound is formed from simple substances, in the standard state (25ºC and 1 atm). For elements in the standard state, the enthalpy of formation is considered zero.

The enthalpy of reaction (ΔHr), on the other hand, is the sum of the enthalpies of formation of the products minus the sum of the enthalpies of formation of the reactants. In other words, it informs us of the amount of energy absorbed or released in a chemical reaction.

Practical Activity

Activity Title: Calculating Enthalpy: From the Laboratory to the World

Project Objective

The project aims to calculate the enthalpy of chemical reactions and understand the theoretical concepts behind enthalpy calculation. The exercise will allow students to experience the calculation of enthalpy in practice and engage in a comprehensive discussion about its implications in other disciplines and the real world.

Detailed Project Description

Each group will be responsible for selecting two exothermic and two endothermic chemical reactions, in which they will calculate the enthalpy. In addition to calculating the enthalpy, each group should contextualize the chosen reactions, identifying where these reactions are applied in the real world and what is the relevance of enthalpy in these situations.

The project will consist of:

1. Selection and description of two exothermic and two endothermic chemical reactions.
2. Performing the enthalpy calculations of the chosen reactions.
3. Contextualizing the reactions, explaining their application in the real world.
4. Preparation of the final report, presenting all the results achieved and the reflections made throughout the project.

Required Materials

• Table of formation enthalpies
• Calculator
• Books and/or internet for research

Detailed Step-by-Step

1. Form groups of three to five students.
2. Each group must select two exothermic and two endothermic chemical reactions.
3. Research the enthalpy of formation of the reactants and products of the reaction.
4. Calculate the enthalpy of the chosen reactions using the enthalpy of reaction formula.
5. Research and contextualize the phenomena and events where these reactions are applied in the real world.
6. Prepare a project report following the detailed guidelines below.

Project Deliverables and Document Writing

As the main project deliverable, groups must prepare a final report divided into four parts: Introduction, Development, Conclusions, and Bibliography.

In the Introduction, the group should contextualize the theme and the project's objectives. Here, the theoretical basis will be recalled, and the project will be presented, justifying the relevance of enthalpy calculation in the context of the studied chemical reactions.

In the Development, the selected reactions should be presented, as well as the enthalpy calculations performed. Additionally, this section should explore the contextualization of the reactions in the real world, explaining when and where they are observed, and the importance of enthalpy calculation for them. The methodology used and the results obtained should also be included in this part.

The Conclusions should address the main points of the work, the lessons learned, and the conclusions drawn about the project, such as the practical application of enthalpy and its relevance in the scientific and real world.

Finally, the Bibliography should list the research sources used.

With the project, it is expected that students acquire technical skills, especially the ability to calculate the enthalpy of chemical reactions and understand its practical application. In addition, socio-emotional skills such as time management, communication, problem-solving, and critical thinking will also be developed.

Remember: clear and concise communication is essential for a good report. Be objective, pay attention to spelling and grammar, and keep the arguments logical and well-organized.