Factors that Contribute to a Positive Enthalpy Change

Oct 13, 2025 by wbrum.org 131 views

Introduction

Enthalpy change is a crucial concept in chemistry that helps us understand the energy changes that occur during chemical reactions. It is a measure of the total energy of a system, including both internal energy and the energy associated with the pressure and volume of a system. In this article, we will explore the concept of enthalpy change and discuss why the enthalpy change of a reaction is positive in certain cases.

What is Enthalpy Change?

Enthalpy change, denoted by ΔH, is the change in enthalpy that occurs during a chemical reaction. It is a measure of the energy change that occurs when reactants are converted into products. Enthalpy change is an important concept in chemistry because it helps us understand the energy changes that occur during chemical reactions.

Types of Enthalpy Change

There are two types of enthalpy change: positive and negative. A positive enthalpy change indicates that energy is absorbed during the reaction, while a negative enthalpy change indicates that energy is released during the reaction.

Why is the Enthalpy Change of the Reaction Positive?

The enthalpy change of the reaction is positive because the reaction involves the breaking of a bond between two oxygen atoms. This process requires energy, which is absorbed from the surroundings, resulting in a positive enthalpy change.

Explanation

The reaction involves the breaking of a bond between two oxygen atoms, resulting in the formation of two oxygen atoms. This process requires energy, which is absorbed from the surroundings. The energy absorbed is in the form of heat, which is released into the surroundings, resulting in a positive enthalpy change.

Factors that Contribute to a Positive Enthalpy Change

There are several factors that contribute to a positive enthalpy change in a reaction. These include:

Breaking of bonds: The breaking of bonds between atoms requires energy, which is absorbed from the surroundings, resulting in a positive enthalpy change.
Formation of new bonds: The formation of new bonds between atoms requires energy, which is absorbed from the surroundings, resulting in a positive enthalpy change.
Increase in the number of moles of gas: An increase in the number of moles of gas in a reaction results in a positive enthalpy change.
Increase in the number of moles of liquid: An increase in the number of moles of liquid in a reaction results in a positive enthalpy change.

Examples of Reactions with Positive Enthalpy Change

There are several examples of reactions that have a positive enthalpy change. These include:

Combustion reactions: Combustion reactions involve the breaking of bonds between atoms and the formation of new bonds between atoms. These reactions require energy, which is absorbed from the surroundings, resulting in a positive enthalpy change.
Decomposition reactions: Decomposition reactions involve the breaking of bonds between atoms and the formation of new bonds between atoms. These reactions require energy, which is absorbed from the surroundings, resulting in a positive enthalpy change.
Synthesis reactions: Synthesis reactions involve the formation of new bonds between atoms. These reactions require energy, which is absorbed from the surroundings, resulting in a positive enthalpy change.

Conclusion

In conclusion, the enthalpy change of a reaction is positive because the reaction involves the breaking of a bond between two oxygen atoms. This process requires energy, which is absorbed from the surroundings, resulting in a positive enthalpy change. Factors that contribute to a positive enthalpy change include the breaking of bonds, the formation of new bonds, an increase in the number of moles of gas, and an increase in the number of moles of liquid.

References

Levine, I. N. (2008). Physical Chemistry. 6th ed. New York: McGraw-Hill.
Atkins, P. W. (2007). Physical Chemistry. 9th ed. New York: Oxford University Press.
Moore, J. W. (2008). Chemistry: The Central Science. 11th ed. New York: Prentice Hall.

Frequently Asked Questions about Enthalpy Change

Q: What is enthalpy change?

A: Enthalpy change, denoted by ΔH, is the change in enthalpy that occurs during a chemical reaction. It is a measure of the energy change that occurs when reactants are converted into products.

Q: What is the difference between enthalpy change and internal energy change?

A: Enthalpy change (ΔH) is the change in enthalpy, which includes both internal energy and the energy associated with the pressure and volume of a system. Internal energy change (ΔU) is the change in internal energy, which only includes the energy associated with the motion of particles and the potential energy of the system.

Q: What are the units of enthalpy change?

A: The units of enthalpy change are typically measured in joules per mole (J/mol) or kilojoules per mole (kJ/mol).

Q: What is the sign of enthalpy change?

A: The sign of enthalpy change indicates whether energy is absorbed or released during the reaction. A positive enthalpy change indicates that energy is absorbed, while a negative enthalpy change indicates that energy is released.

Q: What are some common examples of reactions with positive enthalpy change?

A: Some common examples of reactions with positive enthalpy change include combustion reactions, decomposition reactions, and synthesis reactions.

Q: What are some common examples of reactions with negative enthalpy change?

A: Some common examples of reactions with negative enthalpy change include exothermic reactions, such as the combustion of methane, and endothermic reactions, such as the melting of ice.

Q: How is enthalpy change related to the Gibbs free energy change?

A: The Gibbs free energy change (ΔG) is related to the enthalpy change (ΔH) and the entropy change (ΔS) by the equation: ΔG = ΔH - TΔS. This equation shows that the Gibbs free energy change is a function of both the enthalpy change and the entropy change.

Q: What is the significance of enthalpy change in chemical reactions?

A: Enthalpy change is a crucial concept in chemistry that helps us understand the energy changes that occur during chemical reactions. It is a measure of the total energy of a system, including both internal energy and the energy associated with the pressure and volume of a system.

Q: How can enthalpy change be measured?

A: Enthalpy change can be measured using various techniques, including calorimetry, bomb calorimetry, and differential scanning calorimetry.

Q: What are some common applications of enthalpy change?

A: Enthalpy change has many practical applications in fields such as chemistry, physics, and engineering. Some common applications include:

Thermodynamics: Enthalpy change is used to calculate the energy changes that occur during chemical reactions.
Chemical engineering: Enthalpy change is used to design and optimize chemical processes, such as distillation and reaction kinetics.
Materials science: Enthalpy change is used to study the properties of materials, such as their melting points and boiling points.

Conclusion

In conclusion, enthalpy change is a fundamental concept in chemistry that helps us understand the energy changes that occur during chemical reactions. It is a measure of the total energy of a system, including both internal energy and the energy associated with the pressure and volume of a system. By understanding enthalpy change, we can better design and optimize chemical processes, and gain a deeper understanding of the properties of materials.