Chapter 9, Problem 78E

Interpretation Introduction

Interpretation:

The standard enthalpy change, ΔH° for the following reactions as per exercise 76 and 77 needs to be deduced and a comparison of the energy/kg of the reactant mixture needs to be presented

  ${\text{3Al(s) + 3NH}}_{\text{4}}{\text{ClO}}_{\text{4}}\text{(s) }\to {\text{ Al}}_{\text{2}}{\text{O}}_{\text{3}}{\text{(s) + AlCl}}_{\text{3}}{\text{(s) + 3NO(g) + 6H}}_2\text{O}(g)$

  ${\text{4N}}_{\text{2}}{\text{H}}_{\text{3}}{\text{CH}}_{\text{3}}{\text{(l) + 5N}}_{\text{2}}{\text{O}}_4\text{(l) }\to {\text{ 12H}}_2\text{O}(g)+{\text{9N}}_2{\text{(g) + 4CO}}_2\text{(g)}$

Concept Introduction:

The standard enthalpy change for a reaction ${\text{ΔH}}_{\text{R}}^{\text{0}}$ measured at 298 K and 1 atm is given in terms of the difference in the standard enthalpy of formation of the products and that of reactants.

i.e. ${\text{ΔH}}_{\text{R}}^{\text{0}}\text{ = }{\displaystyle \sum {\text{n}}_{\text{p}}{\text{ΔH}}_{\text{f}}^{\text{0}}}\text{(products) - }{\displaystyle \sum {\text{n}}_{\text{r}}{\text{ΔH}}_{\text{f}}^{\text{0}}}\text{(reactants) ------(1)}$

Here, n_p and n_r are the number of moles of the products and reactants.