Predicting the feasibility of reactions

Oct 13, 2025 by wbrum.org 90 views

Introduction

In chemistry, understanding the thermodynamics of reactions is crucial for predicting their feasibility and spontaneity. One of the key thermodynamic properties that help in this understanding is the enthalpy of formation, which is the change in enthalpy that occurs when one mole of a compound is formed from its constituent elements in their standard states. In this article, we will explore the concept of enthalpy of formation and use it to determine whether a given reaction is endothermic or exothermic.

What is Enthalpy of Formation?

The enthalpy of formation is a measure of the energy change that occurs when a compound is formed from its constituent elements. It is defined as the change in enthalpy (ΔH) that occurs when one mole of a compound is formed from its constituent elements in their standard states. The standard state of an element is its most stable form at a pressure of 1 bar and a temperature of 25°C.

Calculating Enthalpy of Formation

The enthalpy of formation can be calculated using the following equation:

ΔHf = ΔH(products) - ΔH(reactants)

where ΔHf is the enthalpy of formation, ΔH(products) is the enthalpy of the products, and ΔH(reactants) is the enthalpy of the reactants.

The Given Reaction

The given reaction is:

6C(s, graphite) + 3H2(g) → C6H6(l)

The enthalpy of formation for C6H6(l) is given as 49.0 kJ/mol.

Is the Reaction Endothermic or Exothermic?

To determine whether the reaction is endothermic or exothermic, we need to calculate the enthalpy change (ΔH) for the reaction. We can do this by calculating the enthalpy of the products and the reactants and then subtracting the enthalpy of the reactants from the enthalpy of the products.

Calculating the Enthalpy of the Products

The enthalpy of the products is the enthalpy of C6H6(l), which is given as 49.0 kJ/mol.

Calculating the Enthalpy of the Reactants

The enthalpy of the reactants is the sum of the enthalpies of the individual reactants. The enthalpy of C(s, graphite) is 0 kJ/mol, since it is in its standard state. The enthalpy of H2(g) is -285.8 kJ/mol.

Calculating the Enthalpy Change (ΔH)

Now that we have calculated the enthalpy of the products and the reactants, we can calculate the enthalpy change (ΔH) for the reaction.

ΔH = ΔH(products) - ΔH(reactants) = 49.0 kJ/mol - (6 x 0 kJ/mol + 3 x -285.8 kJ/mol) = 49.0 kJ/mol + 857.4 kJ/mol = 906.4 kJ/mol

Conclusion

Since the enthalpy change (ΔH) for the reaction is positive (906.4 kJ/mol), the reaction is endothermic. This means that the reaction requires energy to proceed, and the energy is absorbed from the surroundings.

Discussion

The enthalpy of formation is a crucial thermodynamic property that helps in understanding the feasibility and spontaneity of reactions. In this article, we have used the enthalpy of formation to determine whether a given reaction is endothermic or exothermic. We have calculated the enthalpy change (ΔH) for the reaction and found that it is positive, indicating that the reaction is endothermic.

Applications of Enthalpy of Formation

The enthalpy of formation has numerous applications in chemistry and other fields. Some of the key applications include:

Predicting the feasibility of reactions: The enthalpy of formation can be used to predict whether a reaction is feasible or not. If the enthalpy change (ΔH) for the reaction is negative, the reaction is likely to be spontaneous and feasible.
Designing chemical processes: The enthalpy of formation can be used to design chemical processes that are energy-efficient and cost-effective.
Understanding biological processes: The enthalpy of formation can be used to understand biological processes such as metabolism and respiration.

Limitations of Enthalpy of Formation

While the enthalpy of formation is a useful thermodynamic property, it has some limitations. Some of the key limitations include:

Assuming ideal behavior: The enthalpy of formation assumes ideal behavior of the reactants and products, which may not be the case in real-world scenarios.
Not accounting for non-ideal behavior: The enthalpy of formation does not account for non-ideal behavior of the reactants and products, which can affect the accuracy of the results.
Not considering the effects of pressure and temperature: The enthalpy of formation is typically calculated at standard pressure and temperature, which may not be the case in real-world scenarios.

Conclusion

In conclusion, the enthalpy of formation is a crucial thermodynamic property that helps in understanding the feasibility and spontaneity of reactions. We have used the enthalpy of formation to determine whether a given reaction is endothermic or exothermic and found that it is endothermic. The enthalpy of formation has numerous applications in chemistry and other fields, but it also has some limitations that need to be considered.

References

CRC Handbook of Chemistry and Physics: This reference book provides a comprehensive collection of thermodynamic data, including the enthalpy of formation.
NIST Chemistry WebBook: This online resource provides a comprehensive collection of thermodynamic data, including the enthalpy of formation.
Thermodynamics: An Introduction to the Physical Theories of Equilibrium Thermostatics and Irreversible Thermodynamics: This textbook provides a comprehensive introduction to thermodynamics, including the concept of enthalpy of formation.