Chapter 10, Problem 10.81QP

Specify which compound in each of the following pairs of ionic compounds should have the higher lattice energy: (a) KCl or MgO, (b) LiF or LiBr, (c) Mg₃N₂ or NaCl, (d) AlN or CaO, (e) NaF or CsF, (f) MgCl₂ or MgF₂. Explain your choice.

Interpretation Introduction

Interpretation:

The highest lattice energy among the given pair of ionic compounds has to be identified.

Concept Introduction:

Lattice energy:

The amount of energy that is necessary for the conversion of one mole of ionic solid to its constituent ions in gaseous phase is called Lattice energy.

Hess’s law:

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 called as Hess’s law.

Enthalpy is generally calculated from the standard enthalpy of formation.

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

With the thermodynamic values from Hess’s law, the lattice energy of ionic compound can be determined.

Answer to Problem 10.81QP

$\text{MgO}$ has higher lattice energy.

Explanation of Solution

$\text{MgO}$ has higher lattice energy because the charges are higher and the cation and anion are smaller.

Interpretation Introduction

Interpretation:

The highest lattice energy among the given pair of ionic compounds has to be identified.

Concept Introduction:

Lattice energy:

The amount of energy that is necessary for the conversion of one mole of ionic solid to its constituent ions in gaseous phase is called Lattice energy.

Hess’s law:

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 called as Hess’s law.

Enthalpy is generally calculated from the standard enthalpy of formation.

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

With the thermodynamic values from Hess’s law, the lattice energy of ionic compound can be determined.

Answer to Problem 10.81QP

$\text{LiF}$ has higher lattice energy.

Explanation of Solution

$\text{LiF}$ has higher lattice energy because the anion is smaller whereas the charge remains the same.

Interpretation Introduction

Interpretation:

The highest lattice energy among the given pair of ionic compounds has to be identified.

Concept Introduction:

Lattice energy:

The amount of energy that is necessary for the conversion of one mole of ionic solid to its constituent ions in gaseous phase is called Lattice energy.

Hess’s law:

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 called as Hess’s law.

Enthalpy is generally calculated from the standard enthalpy of formation.

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

With the thermodynamic values from Hess’s law, the lattice energy of ionic compound can be determined.

Answer to Problem 10.81QP

${\text{Mg}}_{\text{3}}{\text{N}}_{\text{2}}$ has higher lattice energy.

Explanation of Solution

${\text{Mg}}_{\text{3}}{\text{N}}_{\text{2}}$ has higher lattice energy because the charges are higher and the total of atomic radii is smaller.

Interpretation Introduction

Interpretation:

The highest lattice energy among the given pair of ionic compounds has to be identified.

Concept Introduction:

Lattice energy:

The amount of energy that is necessary for the conversion of one mole of ionic solid to its constituent ions in gaseous phase is called Lattice energy.

Hess’s law:

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 called as Hess’s law.

Enthalpy is generally calculated from the standard enthalpy of formation.

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

With the thermodynamic values from Hess’s law, the lattice energy of ionic compound can be determined.

Answer to Problem 10.81QP

$\text{NaF}$ has higher lattice energy.

Explanation of Solution

$\text{NaF}$ has higher lattice energy because the charges are higher and the total of atomic radii is smaller.

Interpretation Introduction

Interpretation:

The highest lattice energy among the given pair of ionic compounds has to be identified.

Concept Introduction:

Lattice energy:

The amount of energy that is necessary for the conversion of one mole of ionic solid to its constituent ions in gaseous phase is called Lattice energy.

Hess’s law:

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 called as Hess’s law.

Enthalpy is generally calculated from the standard enthalpy of formation.

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

With the thermodynamic values from Hess’s law, the lattice energy of ionic compound can be determined.

Answer to Problem 10.81QP

$\text{NaF}$ has higher lattice energy.

Explanation of Solution

$\text{NaF}$ has higher lattice energy because the charges are identical whereas the ionic radius of cation is very small.

Interpretation Introduction

Interpretation:

The highest lattice energy among the given pair of ionic compounds has to be identified.

Concept Introduction:

Lattice energy:

The amount of energy that is necessary for the conversion of one mole of ionic solid to its constituent ions in gaseous phase is called Lattice energy.

Hess’s law:

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 called as Hess’s law.

Enthalpy is generally calculated from the standard enthalpy of formation.

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

With the thermodynamic values from Hess’s law, the lattice energy of ionic compound can be determined.

Answer to Problem 10.81QP

${\text{MgF}}_2$ has higher lattice energy.

Explanation of Solution

${\text{MgF}}_2$ has higher lattice energy because the charges are identical whereas the ionic radius of anion is very small.