Q76E - Chemistry (OpenStax)

Question

For which of the following substances is the least energy required to convert one mole of the solid into separate ions? 

(a) \({\rm{MgO}}\) 

(b) \({\rm{SrO}}\) 

(c) \({\rm{KF}}\) 

(d) \({\rm{CsF}}\) 

(e) \({\rm{Mg}}{{\rm{F}}_{\rm{2}}}\)

Step-by-Step Solution

Answer

1. For \(MgO\) the amount energy required to convert one mole of the solid into separate ions is \({\rm{3791\;kJ/mol}}\), which is not the least among others.
2. For \(SrO\) the amount energy required to convert one mole of the solid into separate ions is \({\rm{3223\;kJ/mol}}\), which is not the least among others.
3. For \(KF\) the amount energy required to convert one mole of the solid into separate ions is \({\rm{821\;kJ/mol}}\), which is not the least among others.
4. For \(CsF\) the amount energy required to convert one mole of the solid into separate ions is \({\rm{740\;kJ/mol}}\), which is the least among others.
5. For \({\rm{Mg}}{{\rm{F}}_{\rm{2}}}\) the amount energy required to convert one mole of the solid into separate ions is \({\rm{2957 kJ/mol}}\), which is not the least among others.

Step 1: Concept Introduction

The lattice energy is the change in energy that occurs when one mole of a crystalline ionic compound is formed from its constituent ions, which are considered to be in a gaseous state at the start. It's a metric for the forces that bind ionic solids together.

Step 2: Lattice Energy of Magnesium Oxide

(a)

Lattice energy is defined as energy that is required to convert the solid into separate ions. In order to calculate this, we can take help of Born-Haber cycle.

The values in \({\rm{kJ/mol}}\) for \(MgO\) is \({\rm{3791\;kJ/mol}}\).

 

Therefore, the lattice energy of \(MgO\) is \({\rm{3791\;kJ/mol}}\).

Step 3: Lattice Energy of Strontium Oxide

(b)

Lattice energy is defined as energy that is required to convert the solid into separate ions. In order to calculate this, we can take help of Born-Haber cycle.

The values in \({\rm{kJ/mol}}\) for \(SrO\) is \({\rm{3223\;kJ/mol}}\).

 

Therefore, the lattice energy of \(SrO\) is \({\rm{3223\;kJ/mol}}\).

Step 4: Lattice Energy of Potassium Fluoride

(c)

Lattice energy is defined as energy that is required to convert the solid into separate ions. In order to calculate this, we can take help of Born-Haber cycle.

The values in \({\rm{kJ/mol}}\) for \(KF\) is \({\rm{821\;kJ/mol}}\).

 

Therefore, the lattice energy of \(KF\) is \({\rm{821\;kJ/mol}}\).

Step 5: Lattice Energy of Caesium Fluoride

(d)

Lattice energy is defined as energy that is required to convert the solid into separate ions. In order to calculate this, we can take help of Born-Haber cycle.

The values in \({\rm{kJ/mol}}\) for \(CsF\) is \({\rm{740\;kJ/mol}}\).

 

Therefore, the lattice energy of \(CsF\) is \({\rm{740\;kJ/mol}}\).

Step 6: Lattice Energy of Magnesium Fluoride

(e)

Lattice energy is defined as energy that is required to convert the solid into separate ions. In order to calculate this, we can take help of Born-Haber cycle.

The values in \({\rm{kJ/mol}}\) for \({\rm{Mg}}{{\rm{F}}_{\rm{2}}}\) is \({\rm{2957 kJ/mol}}\).

 

Therefore, the lattice energy of \({\rm{Mg}}{{\rm{F}}_{\rm{2}}}\) is \({\rm{2957 kJ/mol}}\).