Chapter 9, Problem 68E

Interpretation Introduction

Interpretation:

The enthalpy of reaction using bond energy values is to be calculated.
The reason as to why the enthalpy of formation of $\text{HBr}$ is not equal to one-half of the value calculated is to be accounted.

Concept introduction: Bond energy or bond enthalpy is the amount of energy required to break one mole of bonds. Breaking of bonds is an endothermic reaction because energy is always absorbed in the process and its value is always positive. Formation of bonds is an exothermic reaction because energy is always released in the process and its value is always negative.
The enthalpy of a reaction is calculated by the formula,

$\text{Δ}{H}_{\text{rxn}}={\displaystyle \sum \left(\text{Δ}{H}_{\text{bonds}\text{broken}}\right)}+{\displaystyle \sum \left(\text{Δ}{H}_{\text{bonds}\text{formed}}\right)}$

To determine: The enthalpy of reaction using bond energy values and the reason as to why the enthalpy of formation of $\text{HBr}$ is not equal to one-half of the value calculated.