Understanding Enthalpy of Formation

Oct 13, 2025 by pynkocean.com 14 views

Introduction

Hydrogen chloride (HCl) is a highly reactive and corrosive gas that plays a crucial role in various industrial processes. It is formed through the reaction between hydrogen gas (H2) and chlorine gas (Cl2). In this article, we will delve into the details of this reaction, exploring the thermodynamic properties of hydrogen chloride and determining the correct statement regarding the reaction.

The Reaction

The reaction between hydrogen gas and chlorine gas to form hydrogen chloride is represented by the following equation:

${ H_2(g) + Cl_2(g) \rightarrow 2 \, HCl(g) }$

This reaction is highly exothermic, releasing a significant amount of energy in the form of heat. The standard enthalpy of formation ( ${\Delta H_f}$ ) for hydrogen chloride is -92.3 kJ/mol, indicating that the reaction is highly favorable and releases a substantial amount of energy.

Understanding Enthalpy of Formation

The enthalpy of formation ( ${\Delta H_f}$ ) is a measure of the energy change that occurs when one mole of a substance is formed from its constituent elements in their standard states. In the case of hydrogen chloride, the enthalpy of formation is -92.3 kJ/mol, indicating that the formation of one mole of HCl gas releases 92.3 kJ of energy.

Determining the Correct Statement

Given the reaction equation and the enthalpy of formation for hydrogen chloride, we can now determine the correct statement regarding the reaction.

Statement 1: The reaction between hydrogen gas and chlorine gas to form hydrogen chloride is highly endothermic.

Statement 2: The reaction between hydrogen gas and chlorine gas to form hydrogen chloride is highly exothermic.

Statement 3: The enthalpy of formation for hydrogen chloride is 92.3 kJ/mol.

Statement 4: The reaction between hydrogen gas and chlorine gas to form hydrogen chloride is not spontaneous.

Analysis

To determine the correct statement, let's analyze each option:

Statement 1: The reaction between hydrogen gas and chlorine gas to form hydrogen chloride is highly endothermic. This statement is incorrect because the reaction is highly exothermic, releasing a significant amount of energy in the form of heat.
Statement 2: The reaction between hydrogen gas and chlorine gas to form hydrogen chloride is highly exothermic. This statement is correct because the reaction releases a substantial amount of energy in the form of heat, as indicated by the negative enthalpy of formation.
Statement 3: The enthalpy of formation for hydrogen chloride is 92.3 kJ/mol. This statement is incorrect because the enthalpy of formation is -92.3 kJ/mol, indicating that the formation of one mole of HCl gas releases 92.3 kJ of energy.
Statement 4: The reaction between hydrogen gas and chlorine gas to form hydrogen chloride is not spontaneous. This statement is incorrect because the reaction is highly favorable and releases a significant amount of energy, indicating that it is spontaneous.

Conclusion

In conclusion, the correct statement regarding the reaction between hydrogen gas and chlorine gas to form hydrogen chloride is that the reaction is highly exothermic. This is indicated by the negative enthalpy of formation for hydrogen chloride, which shows that the formation of one mole of HCl gas releases 92.3 kJ of energy.

References

Petrucci, R. H., Harwood, W. S., Herring, F. G., & Madura, J. D. (2016). General chemistry: Principles and modern applications. Pearson Education.
Atkins, P. W., & De Paula, J. (2010). Physical chemistry. Oxford University Press.