(b) Table 1 Contains Some Standard Enthalpy Of Formation Data.$\[ \begin{tabular}{|c|c|c|} \hline \multicolumn{1}{|c|}{\textbf{Table 1}} \\ \hline & $CO(g)$ & $Fe_2O_3(s)$ \\ \hline $\Delta_f H^{\circ} / \text{kJ Mol}^{-1}$ & -111 & -822

Feb 25, 2025 by ADMIN 238 views

**Understanding Standard Enthalpy of Formation: A Comprehensive Guide**

Introduction

In the realm of chemistry, thermodynamics plays a crucial role in understanding the behavior of substances. One of the fundamental concepts in thermodynamics is the standard enthalpy of formation, denoted by $\Delta_f H^{\circ}$ . This property is a measure of the change in enthalpy that occurs when one mole of a substance is formed from its constituent elements in their standard states. In this article, we will delve into the concept of standard enthalpy of formation, its significance, and how it is used in various chemical reactions.

What is Standard Enthalpy of Formation?

Standard enthalpy of formation is a measure of the change in enthalpy that occurs when one mole of a substance is formed from its constituent elements in their standard states. The standard state of an element is defined as the state in which the element exists at a pressure of 1 bar and a temperature of 25°C. The standard enthalpy of formation is denoted by $\Delta_f H^{\circ}$ and is typically expressed in units of kJ/mol.

Importance of Standard Enthalpy of Formation

The standard enthalpy of formation is an important property in chemistry because it provides valuable information about the energy changes that occur during chemical reactions. By knowing the standard enthalpy of formation of a substance, chemists can predict the energy changes that will occur when the substance is formed or decomposed. This information is crucial in understanding the spontaneity of chemical reactions and the feasibility of chemical processes.

Table 1: Standard Enthalpy of Formation Data

Substance	$\Delta_f H^{\circ} / \text{kJ mol}^{-1}$
$CO(g)$	-111
$Fe_2O_3(s)$	-822

Interpretation of Standard Enthalpy of Formation Data

The standard enthalpy of formation data in Table 1 provides valuable information about the energy changes that occur when one mole of $CO(g)$ and $Fe_2O_3(s)$ are formed from their constituent elements in their standard states. The negative value of $\Delta_f H^{\circ}$ for $CO(g)$ indicates that the formation of $CO(g)$ is an exothermic process, releasing energy into the surroundings. On the other hand, the negative value of $\Delta_f H^{\circ}$ for $Fe_2O_3(s)$ indicates that the formation of $Fe_2O_3(s)$ is also an exothermic process, releasing energy into the surroundings.

Calculating Standard Enthalpy of Reaction

The standard enthalpy of reaction is a measure of the change in enthalpy that occurs during a chemical reaction. It can be calculated using the standard enthalpy of formation data of the reactants and products. The standard enthalpy of reaction is denoted by $\Delta_r H^{\circ}$ and is typically expressed in units of kJ/mol.

Example: Calculating the Standard Enthalpy of Reaction for the Formation of $CO(g)$

Suppose we want to calculate the standard enthalpy of reaction for the formation of $CO(g)$ from its constituent elements in their standard states. The standard enthalpy of formation data for $CO(g)$ is -111 kJ/mol. The standard enthalpy of formation data for $C(s)$ and $O_2(g)$ are 0 kJ/mol and 0 kJ/mol, respectively.

The balanced chemical equation for the formation of $CO(g)$ is:

C(s) + \frac{1}{2}O_2(g) \rightarrow CO(g)

The standard enthalpy of reaction for this reaction can be calculated as follows:

\Delta_r H^{\circ} = \Delta_f H^{\circ}(CO(g)) - \Delta_f H^{\circ}(C(s)) - \frac{1}{2}\Delta_f H^{\circ}(O_2(g))

\Delta_r H^{\circ} = -111\text{ kJ/mol} - 0\text{ kJ/mol} - \frac{1}{2}(0\text{ kJ/mol})

\Delta_r H^{\circ} = -111\text{ kJ/mol}

Therefore, the standard enthalpy of reaction for the formation of $CO(g)$ is -111 kJ/mol.

Conclusion

In conclusion, the standard enthalpy of formation is an important property in chemistry that provides valuable information about the energy changes that occur during chemical reactions. By knowing the standard enthalpy of formation of a substance, chemists can predict the energy changes that will occur when the substance is formed or decomposed. The standard enthalpy of reaction can be calculated using the standard enthalpy of formation data of the reactants and products. This information is crucial in understanding the spontaneity of chemical reactions and the feasibility of chemical processes.

References

Atkins, P. W., & de Paula, J. (2010). Physical chemistry (9th ed.). Oxford University Press.
Chang, R. (2010). Chemistry: The central science (11th ed.). McGraw-Hill.
Levine, I. N. (2012). Physical chemistry (6th ed.). McGraw-Hill.