Contextualization

Enthalpy, also known as H, is a thermodynamic state function, which in open systems corresponds to the internal energy plus the product of pressure and volume. It is a physical quantity that is not directly measured, but can be calculated from the bonding energies of the reactants and products of a chemical reaction.

Chemical Bonding

Chemical bonds occur when atoms come together to form molecules. This results in systems with lower energy, therefore more stable. The energy required to break a molecule into isolated atoms is the bonding energy. During the process of forming a molecule from isolated atoms, this energy is released.

Enthalpy and Bonding Energies

In terms of bonding energies, we can say that the total enthalpy of a molecule is the sum of the energies of the bonds that compose it. For a chemical reaction, the ∆H of the reaction is the energy required to break all the bonds of the reactants minus the energy released when forming all the bonds of the products.

Enthalpy has very important applications in the real world. It is used to calculate the energy released or absorbed in a chemical process, which is extremely important in sectors such as energy and food production. In addition, enthalpy can provide us with information about the stability of a molecule, which can be useful in the production of new materials and medicines.

Learning about enthalpy and bonding energies will not only provide you with a deeper understanding of chemical processes, but also open doors to a variety of interesting fields of research and innovation.

Practical Activity: Coffee Heater: Enthalpy in Practice

Project Objective

The activity aims to measure the ∆H of a chemical reaction and, from that, determine the bonding energies of the reactants and products of the reaction. For this, students will use the reaction between sodium bicarbonate and hydrochloric acid to heat a known amount of water. Additionally, students should prepare a report to present the theory, methodology, results, and conclusion of the project.

Detailed Project Description

Students will be divided into groups of 3 to 5 people and will have one week to complete the project.

The experiment consists of measuring the initial temperature of the water, adding the combination of sodium bicarbonate and hydrochloric acid, which will react and release heat, and measuring the final temperature of the water. Using the enthalpy equation (∆H = Q/n), with Q being the transferred energy and n the number of moles of the reaction, they will be able to calculate the ∆H of the reaction.

With the ∆H in hand, students will be able to use the bonding energies of the reactants and products (data that will be provided) to confirm if the calculated ∆H is correct.

Required Materials

For the experiment, the following materials will be needed:

• Sodium bicarbonate
• Hydrochloric acid
• Water
• Beaker
• Scale
• Thermometer
• Calculator

Step by Step

1. Weigh 5 grams of sodium bicarbonate and set aside.
2. Fill the beaker with 100ml of water.
3. Measure and record the initial temperature of the water.
4. Add 10 ml of hydrochloric acid to the sodium bicarbonate and quickly mix with the water.
5. Observe the reaction and measure as the water temperature increases.
6. When the temperature stops rising, measure and record the final temperature of the water.
7. Calculate the energy transferred to the water.
8. Calculate the ∆H of the reaction.
9. Compare the calculated ∆H with the theoretical value.

Students should record all observations, measurements, and calculations made during the experiment to include in their report.

Project Deliverables

At the end of the project, each group must submit a report containing:

1. Introduction: Contextualization on the theme of enthalpy and bonding energy, their real-world applications, and the importance of this knowledge for society and the field of chemistry. It should also state the project's objective.

2. Development: Detailed description of the practical activity, including the methodology used, the materials, and the observations made during the experiment. It should also contain the theoretical foundation of the experiment, explaining the theory of enthalpy and bonding energy, and present the calculations and results obtained.

3. Conclusion: Recap of the main points of the work, the learnings obtained, and the conclusions about the experiment. It should also include a comparison between the experimental and theoretical results and a discussion on the possible sources of error in the experiment.

4. Bibliography: Bibliographic references consulted during the project execution and report elaboration.