Understanding Enthalpy of Combustion

Oct 13, 2025 by wbrum.org 98 views

Introduction

In this article, we will calculate the enthalpy of combustion of 1 mole of acetylene for the given reaction. The reaction is: $2 C_2 H_2 + 5 O_2 \rightarrow 4 CO_2 + 2 H_2 O$ . We will use the information in the table to determine the enthalpy of combustion.

Understanding Enthalpy of Combustion

The enthalpy of combustion is the change in enthalpy that occurs when a substance undergoes combustion. It is a measure of the energy released or absorbed during the combustion reaction. In this case, we are interested in calculating the enthalpy of combustion of 1 mole of acetylene.

The Reaction

The reaction is: $2 C_2 H_2 + 5 O_2 \rightarrow 4 CO_2 + 2 H_2 O$ . This reaction involves the combustion of acetylene (C2H2) in the presence of oxygen (O2) to produce carbon dioxide (CO2) and water (H2O).

The Table

The table provides the following information:

Substance	Enthalpy of Formation (kJ/mol)
C2H2	-226.73
O2	0
CO2	-393.51
H2O	-285.83

Calculating the Enthalpy of Combustion

To calculate the enthalpy of combustion, we need to determine the change in enthalpy that occurs during the reaction. We can do this by calculating the enthalpy of the products and subtracting the enthalpy of the reactants.

Step 1: Calculate the Enthalpy of the Products

The products of the reaction are 4 CO2 and 2 H2O. We can calculate the enthalpy of the products by multiplying the enthalpy of formation of each product by the number of moles.

Enthalpy of products = (4 x -393.51) + (2 x -285.83) Enthalpy of products = -1574.04 + -571.66 Enthalpy of products = -2145.70 kJ/mol

Step 2: Calculate the Enthalpy of the Reactants

The reactants of the reaction are 2 C2H2 and 5 O2. We can calculate the enthalpy of the reactants by multiplying the enthalpy of formation of each reactant by the number of moles.

Enthalpy of reactants = (2 x -226.73) + (5 x 0) Enthalpy of reactants = -453.46 + 0 Enthalpy of reactants = -453.46 kJ/mol

Step 3: Calculate the Enthalpy of Combustion

Now that we have calculated the enthalpy of the products and the reactants, we can calculate the enthalpy of combustion by subtracting the enthalpy of the reactants from the enthalpy of the products.

Enthalpy of combustion = Enthalpy of products - Enthalpy of reactants Enthalpy of combustion = -2145.70 - (-453.46) Enthalpy of combustion = -1692.24 kJ/mol

Conclusion

In this article, we calculated the enthalpy of combustion of 1 mole of acetylene for the reaction: $2 C_2 H_2 + 5 O_2 \rightarrow 4 CO_2 + 2 H_2 O$ . We used the information in the table to determine the enthalpy of combustion. The enthalpy of combustion is -1692.24 kJ/mol.

References

[1] CRC Handbook of Chemistry and Physics, 97th Edition.
[2] Lide, D. R. (2016). CRC Handbook of Chemistry and Physics. CRC Press.

Introduction
Understanding Enthalpy of Combustion
The Reaction
The Table
Calculating the Enthalpy of Combustion
Step 1: Calculate the Enthalpy of the Products
Step 2: Calculate the Enthalpy of the Reactants
Step 3: Calculate the Enthalpy of Combustion
Conclusion
References
Table of Contents
Frequently Asked Questions (FAQs) about Enthalpy of Combustion ====================================================================

Q: What is enthalpy of combustion?

A: Enthalpy of combustion is the change in enthalpy that occurs when a substance undergoes combustion. It is a measure of the energy released or absorbed during the combustion reaction.

Q: Why is enthalpy of combustion important?

A: Enthalpy of combustion is important because it helps us understand the energy released or absorbed during a combustion reaction. This information is crucial in various fields such as chemistry, physics, and engineering.

Q: How is enthalpy of combustion calculated?

A: Enthalpy of combustion is calculated by determining the change in enthalpy that occurs during a combustion reaction. This involves calculating the enthalpy of the products and subtracting the enthalpy of the reactants.

Q: What are the units of enthalpy of combustion?

A: The units of enthalpy of combustion are typically measured in kilojoules per mole (kJ/mol).

Q: Can enthalpy of combustion be negative or positive?

A: Yes, enthalpy of combustion can be either negative or positive. A negative enthalpy of combustion indicates that energy is released during the combustion reaction, while a positive enthalpy of combustion indicates that energy is absorbed.

Q: How does enthalpy of combustion relate to the heat of combustion?

A: Enthalpy of combustion and heat of combustion are related but distinct concepts. Enthalpy of combustion is a measure of the change in enthalpy during a combustion reaction, while heat of combustion is a measure of the energy released or absorbed during the reaction.

Q: Can enthalpy of combustion be used to predict the spontaneity of a reaction?

A: Yes, enthalpy of combustion can be used to predict the spontaneity of a reaction. A negative enthalpy of combustion indicates that the reaction is spontaneous, while a positive enthalpy of combustion indicates that the reaction is non-spontaneous.

Q: How does enthalpy of combustion relate to the Gibbs free energy of a reaction?

A: Enthalpy of combustion and Gibbs free energy are related but distinct concepts. Enthalpy of combustion is a measure of the change in enthalpy during a reaction, while Gibbs free energy is a measure of the energy available to do work during the reaction.

Q: Can enthalpy of combustion be used to predict the rate of a reaction?

A: No, enthalpy of combustion cannot be used to predict the rate of a reaction. The rate of a reaction is influenced by various factors such as the concentration of reactants, temperature, and catalysts.

Q: How does enthalpy of combustion relate to the entropy of a reaction?

A: Enthalpy of combustion and entropy are related but distinct concepts. Enthalpy of combustion is a measure of the change in enthalpy during a reaction, while entropy is a measure of the disorder or randomness of a system.

Q: Can enthalpy of combustion be used to predict the stability of a compound?

A: Yes, enthalpy of combustion can be used to predict the stability of a compound. A negative enthalpy of combustion indicates that the compound is stable, while a positive enthalpy of combustion indicates that the compound is unstable.

Q: How does enthalpy of combustion relate to the bond energy of a compound?

A: Enthalpy of combustion and bond energy are related but distinct concepts. Enthalpy of combustion is a measure of the change in enthalpy during a reaction, while bond energy is a measure of the energy required to break a chemical bond.

Q: Can enthalpy of combustion be used to predict the reactivity of a compound?

A: Yes, enthalpy of combustion can be used to predict the reactivity of a compound. A negative enthalpy of combustion indicates that the compound is reactive, while a positive enthalpy of combustion indicates that the compound is non-reactive.

Conclusion

In this article, we have answered some of the most frequently asked questions about enthalpy of combustion. We hope that this information has been helpful in understanding the concept of enthalpy of combustion and its applications in various fields.