Chapter 9.10, Problem 1RC

Interpretation Introduction

Interpretation:

The reason for calculation of $\Delta H_{rxn}^{°}$ using bond enthalpies not always agreeing with that of $\Delta H_{rxn}^{°}$ calculated using $\Delta H_f^{°}$ values has to be explained.

Concept Introduction:

$\Delta H°$ refers to change in enthalpy.  Change in enthalpy in a reaction and bond energy (BE) are related as,

$\text{ΔH°}\text{=}\text{ΣBE(reactants)-ΣBE(products)}$

Change in enthalpy in a reaction and enthalpy of formation are related by the formula,

$\Delta H_{rxn}^{°}=\Sigma \Delta H_f^{°}(product)-\Sigma \Delta H_f^{°}(reac\tan t)$

Where,

$\begin{array}{l}\Delta H_{rxn}^{°}=\text{ standard}\text{enthalpy change in reaction}\\ \Delta H_f^{°}(product)=\text{ standard}\text{enthalpy of formation of product}\\ \Delta H_f^{°}(reac\tan t)=\text{ standard}\text{enthalpy of formation of }reac\tan t\end{array}$