Chapter 9, Problem 9.114SP

Interpretation Introduction

Interpretation:

$\Delta H°$ of the given reaction has to be calculated using lattice energy of $KCl,$ ionization of energy of K and electron affinity of Cl.

Concept Introduction:

The energy released when gaseous state ions of unlike charges that are infinitely farther apart combine to form a stable ionic solid is called Lattice energy.  Conversely, the energy required to break the electrostatic force of attraction between the ions of unlike charges in the ionic solid and revert them to gaseous state is also termed as Lattice energy of an ionic solid.

Ionization energy is defined as the energy required to remove the valence electron of an atom when it is in gaseous state.  In periodic table ionization energy of elements decreases down the column or group and increases across the row or period as it is inversely proportional to the atomic size.

Electron affinity is defined as the energy released when an electron is added (gained by an atom) to the atom in its gaseous state forming negative ion.  In periodic table electron affinity of elements decreases down the column or group and increases across the row or period as it is inversely proportional to the atomic size.

The enthalpy change that occurs during a chemical transformation is called as enthalpy change of that reaction.

Hess’s law is applied to calculate the enthalpy changes in a reaction.  According to Hess’s law – “The overall enthalpy change of a reaction is equal to the sum of the enthalpy changes involving in each and every individual steps in the reaction.”  Thus if a reaction involves ‘n’ steps then enthalpy change $\Delta H°$ of the reaction is,

  $\Delta H°=\Delta {\text{H}}_1^{°}+\Delta {\text{H}}_2^{°}+\Delta {\text{H}}_3^{°}\mathrm{....}+\Delta {\text{H}}_n^{°}$