Chapter 10, Problem 10.43QP

Interpretation Introduction

Interpretation: Hess’s law and its usefulness in thermochemistry have to be explained.

Concept Introduction:

The enthalpy change for given set of reactants to the given set of products is the same, whether the process takes place in single or sequence of steps.  This is known as Hess’s law.

Enthalpy is generally calculated from the standard enthalpy of formation.

${\text{ΔH°}}_{\text{reaction}}\text{=}\sum {\text{n}}_{\text{p}}{\text{ΔH}}^{\text{°}}{}_{\text{f}}\text{(products)-}\sum {\text{n}}_{\text{p}}{\text{ΔH}}^{\text{°}}\text{(reactants)}$

In thermochemistry, it is used to determine the lattice energy of ionic compounds.