Chapter 9, Problem 9.44P

Interpretation Introduction

Interpretation:

The discrepancy between an enthalpy of reaction obtained from calorimetry and one obtained from bond energies is to be determined.

Concept introduction:

Bond energy is the amount of energy needed to break a bond between two gaseous atoms. Bond energy is measured in $\text{kJ/mol}$ and the standard enthalpy of formation $\left(\Delta H_{\text{f}}^{°}\right)$ is the enthalpy change of the formation of $1\text{mol}$ of compound from its elements and the reactants and products, in this case, is also present in their standard state.

Standard state includes $1\text{atm}$ pressure for gases, $1M$ concentration for substances in the aqueous phase and the most stable form of substance at $1\text{atm}$ pressure and $298\text{K}$ temperature. For example, metal like sodium exists in solid state and molecular elements like halogen exist in a gaseous state.