Welcome budding Chemists! We're about to embark on a journey into the fascinating concept of Hess’s Law. But before we dive in, let's discuss the importance of this principle.
Hess’s Law, named after the Swiss-Russian chemist, Germain Hess, is a foundational principle in the field of Chemistry. It states that the total enthalpy change during the complete course of a chemical reaction is the same whether the reaction is made in one step or in several steps. This law reveals the interrelationship between different chemical reactions, and often makes it possible to calculate the heat of one reaction from the heats of a number of other reactions.
Hess’s Law is both a central and practical concept in Chemistry since it allows us to calculate the enthalpy changes of complex chemical reactions that would otherwise be difficult (or impossible) to measure directly. Therefore, understanding Hess’s Law is not only pivotal for your academic studies, but it forms a cornerstone for those considering careers in natural sciences, pharmaceuticals, energy and climate science.
Now, you must be wondering how we can apply Hess’s Law in our daily lives. Consider a simple example, such as the combustion of gasoline in a car engine. The changes in enthalpy during the various steps of combustion can be calculated using Hess’s Law, helping engineers to design efficient engines. Similarly, Hess’s Law is used in environmental science to calculate the heat changes in various atmospheric reactions.
To delve deeper into Hess's Law and its application, we recommend these reliable resources for your reference:
- Chemistry LibreTexts - Hess's Law
- Khan Academy - Hess's law and reaction enthalpy change
- BBC Bitesize - Hess's Law
Now, let's investigate Hess’s Law together and have some fun in the process!
Activity Title: Hess’s Law in Action: Unraveling the Enthalpy of Combustion
Objective of the Project:
The objective of this project is to practically apply Hess’s Law to calculate the enthalpy change of the combustion of a fuel (e.g. methanol).
Description of the Project:
In groups of 3 to 5, you will carry out a series of reactions to observe Hess's Law in action. You will measure the heat absorbed or released by reactions to calculate the enthalpy change. The ultimate goal is to know how Hess’s Law can be used to determine the enthalpy change of a reaction that is difficult to measure directly.
- Calorimeter (It can be as simple as a Styrofoam cup)
- Digital thermometer
- Methanol (fuel)
- Stand and clamp
- Weighing scale
Detailed Steps for Carrying Out the Activity:
As a group, discuss and draft a plan to measure the heat absorbed or released by reactions involving methanol.
Measure 100g of water and pour it into the calorimeter.
Record the initial temperature of the water.
Weigh a certain amount of methanol fuel before combustion.
Burn the methanol under the calorimeter, ensuring the flame touches the bottom of the calorimeter cup.
Stir the water gently with the thermometer to ensure even heat distribution.
Continuously record the temperature changes until the temperature starts dropping.
Extinguish the flame and reweigh the remaining methanol fuel.
Calculate the heat absorbed by the water and consequently, the heat released by the combustion of methanol.
Repeat the experiment a few times to collect a set of data.
After collecting your data, use the Hess's Law to calculate the enthalpy change for the combustion of methanol.
At the end of this project, you're expected to submit a written report, including the following sections:
Introduction: Here, provide a brief overview of Hess's Law, its relevance, and how it applies to everyday life. State the objective of this project and its connection with Hess's Law.
Development: In this section, detail how you carried out the experiment including the steps taken, the data collected, and the calculations. Discuss how Hess's Law was used to calculate the enthalpy change and provide a step-by-step breakdown of these calculations. Include any challenges encountered during the experiment and how your group solved them. Make sure to present all necessary charts, tables, or graphs used in your calculations.
Conclusion: Summarize the main findings of your experiment and discuss what you have learned about Hess's Law and the concept of enthalpy. Discuss the value and the implications of your findings.
Bibliography: List all the resources you have used to conduct your experiment and write your report.
Remember, this project is not only about demonstrating your understanding of Hess's Law but also about how you cooperate with your team, manage time, and overcome challenges. Good luck, chemists!