Chapter 4, Problem 4.31NP

Interpretation Introduction

Interpretation:

The standard enthalpy of formation ${\text{ΔH}}_{\text{f}}^{\text{0}}$ of benzene needs to be calculated from the tabulated values of the enthalpy of combustion of benzene and enthalpies of formation of CO₂(g) and H₂O(l)

Concept Introduction:

The standard enthalpy of formation ${\text{ΔH}}_{\text{f}}^{\text{0}}$ of a compound is the enthalpy change due to the formation of 1 mole of a compound from its constituent elements in their standard state

Hess's law of constant heat summation states that the total enthalpy change for a given reaction can be expressed as a sum of the enthalpies of the intermediate reactions i.e.

  ${\text{ΔH = ΔH}}_1{\text{+ ΔH}}_2+{\text{ΔH}}_3+\mathrm{....}+{\text{ΔH}}_{\text{n}}\text{ -----(1)}$

Here, ΔH = total enthalpy change

ΔH₁, ΔH₂... ΔH_n are the enthalpy changes of the intermediate steps.